[MINOR] Fix javadoc issues when performing release:prepare

The maven-javadoc-plugin was complaining with 'javadoc: error -
No public or protected classes found to document.' when running
maven release:prepare.
diff --git a/streaming-akka/src/main/scala/org/apache/spark/streaming/akka/package-info.java b/streaming-akka/src/main/scala/org/apache/spark/streaming/akka/package-info.java
deleted file mode 100644
index f2036f4..0000000
--- a/streaming-akka/src/main/scala/org/apache/spark/streaming/akka/package-info.java
+++ /dev/null
@@ -1,21 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-/**
- * Akka receiver for Spark Streaming.
- */
-package org.apache.spark.streaming.akka;
diff --git a/streaming-akka/src/main/scala/org/apache/spark/streaming/akka/package.scala b/streaming-akka/src/main/scala/org/apache/spark/streaming/akka/package.scala
deleted file mode 100644
index c7443ea..0000000
--- a/streaming-akka/src/main/scala/org/apache/spark/streaming/akka/package.scala
+++ /dev/null
@@ -1,23 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.apache.spark.streaming
-
-/**
- * Akka receiver for Spark Streaming.
- */
-package object akka
diff --git a/streaming-mqtt/src/main/scala/org/apache/spark/streaming/mqtt/package-info.java b/streaming-mqtt/src/main/scala/org/apache/spark/streaming/mqtt/package-info.java
deleted file mode 100644
index 290fb09..0000000
--- a/streaming-mqtt/src/main/scala/org/apache/spark/streaming/mqtt/package-info.java
+++ /dev/null
@@ -1,21 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-/**
- * MQTT receiver for Spark Streaming.
- */
-package org.apache.spark.streaming.mqtt;
diff --git a/streaming-mqtt/src/main/scala/org/apache/spark/streaming/mqtt/package.scala b/streaming-mqtt/src/main/scala/org/apache/spark/streaming/mqtt/package.scala
deleted file mode 100644
index 63d0d13..0000000
--- a/streaming-mqtt/src/main/scala/org/apache/spark/streaming/mqtt/package.scala
+++ /dev/null
@@ -1,23 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.apache.spark.streaming
-
-/**
- * MQTT receiver for Spark Streaming.
- */
-package object mqtt
diff --git a/streaming-twitter/src/main/scala/org/apache/spark/streaming/twitter/package-info.java b/streaming-twitter/src/main/scala/org/apache/spark/streaming/twitter/package-info.java
deleted file mode 100644
index 115dd7f..0000000
--- a/streaming-twitter/src/main/scala/org/apache/spark/streaming/twitter/package-info.java
+++ /dev/null
@@ -1,21 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-/**
- * Twitter feed receiver for spark streaming.
- */
-package org.apache.spark.streaming.twitter;
diff --git a/streaming-twitter/src/main/scala/org/apache/spark/streaming/twitter/package.scala b/streaming-twitter/src/main/scala/org/apache/spark/streaming/twitter/package.scala
deleted file mode 100644
index 580e37f..0000000
--- a/streaming-twitter/src/main/scala/org/apache/spark/streaming/twitter/package.scala
+++ /dev/null
@@ -1,23 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.apache.spark.streaming
-
-/**
- * Twitter feed receiver for spark streaming.
- */
-package object twitter
diff --git a/streaming-zeromq/src/main/scala/org/apache/spark/streaming/zeromq/package-info.java b/streaming-zeromq/src/main/scala/org/apache/spark/streaming/zeromq/package-info.java
deleted file mode 100644
index 0401b3f..0000000
--- a/streaming-zeromq/src/main/scala/org/apache/spark/streaming/zeromq/package-info.java
+++ /dev/null
@@ -1,21 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-/**
- * Zeromq receiver for spark streaming.
- */
-package org.apache.spark.streaming.zeromq;
diff --git a/streaming-zeromq/src/main/scala/org/apache/spark/streaming/zeromq/package.scala b/streaming-zeromq/src/main/scala/org/apache/spark/streaming/zeromq/package.scala
deleted file mode 100644
index 65e6e57..0000000
--- a/streaming-zeromq/src/main/scala/org/apache/spark/streaming/zeromq/package.scala
+++ /dev/null
@@ -1,23 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.apache.spark.streaming
-
-/**
- * Zeromq receiver for spark streaming.
- */
-package object zeromq