Remove httpclient dependency. (#655)

* was present for Hadoop 1, which we don't support anymore
* was present for ThreadSafe note on our maven-plugin mojo, but that annotation is gone in current releases

Tested via running ITs locally and against a standalone hadoop 2 cluster
diff --git a/pom.xml b/pom.xml
index 1db8f76..f318381 100644
--- a/pom.xml
+++ b/pom.xml
@@ -39,10 +39,6 @@
       <artifactId>accumulo-minicluster</artifactId>
     </dependency>
     <dependency>
-      <groupId>org.apache.httpcomponents</groupId>
-      <artifactId>httpclient</artifactId>
-    </dependency>
-    <dependency>
       <groupId>org.apache.maven</groupId>
       <artifactId>maven-artifact</artifactId>
     </dependency>
diff --git a/src/it/plugin-test/pom.xml b/src/it/plugin-test/pom.xml
index 9f16afa..175433c 100644
--- a/src/it/plugin-test/pom.xml
+++ b/src/it/plugin-test/pom.xml
@@ -52,10 +52,6 @@
       <artifactId>commons-configuration</artifactId>
     </dependency>
     <dependency>
-      <groupId>commons-httpclient</groupId>
-      <artifactId>commons-httpclient</artifactId>
-    </dependency>
-    <dependency>
       <groupId>commons-io</groupId>
       <artifactId>commons-io</artifactId>
     </dependency>
diff --git a/src/main/java/org/apache/accumulo/maven/plugin/StartMojo.java b/src/main/java/org/apache/accumulo/maven/plugin/StartMojo.java
index 6c504ef..6ec32e5 100644
--- a/src/main/java/org/apache/accumulo/maven/plugin/StartMojo.java
+++ b/src/main/java/org/apache/accumulo/maven/plugin/StartMojo.java
@@ -26,7 +26,6 @@
 import org.apache.accumulo.minicluster.impl.MiniAccumuloClusterImpl;
 import org.apache.accumulo.minicluster.impl.MiniAccumuloConfigImpl;
 import org.apache.commons.io.FileUtils;
-import org.apache.http.annotation.ThreadSafe;
 import org.apache.maven.plugin.MojoExecutionException;
 import org.apache.maven.plugins.annotations.LifecyclePhase;
 import org.apache.maven.plugins.annotations.Mojo;
@@ -36,7 +35,6 @@
 /**
  * Goal which starts an instance of {@link MiniAccumuloCluster}.
  */
-@ThreadSafe
 @Mojo(name = "start", defaultPhase = LifecyclePhase.PRE_INTEGRATION_TEST,
     requiresDependencyResolution = ResolutionScope.TEST)
 public class StartMojo extends AbstractAccumuloMojo {
diff --git a/src/main/java/org/apache/accumulo/maven/plugin/StopMojo.java b/src/main/java/org/apache/accumulo/maven/plugin/StopMojo.java
index af82633..fb96088 100644
--- a/src/main/java/org/apache/accumulo/maven/plugin/StopMojo.java
+++ b/src/main/java/org/apache/accumulo/maven/plugin/StopMojo.java
@@ -19,7 +19,6 @@
 import org.apache.accumulo.minicluster.MiniAccumuloCluster;
 import org.apache.accumulo.minicluster.impl.MiniAccumuloClusterImpl;
 import org.apache.accumulo.minicluster.impl.MiniAccumuloClusterImpl.LogWriter;
-import org.apache.http.annotation.ThreadSafe;
 import org.apache.maven.plugin.MojoExecutionException;
 import org.apache.maven.plugins.annotations.LifecyclePhase;
 import org.apache.maven.plugins.annotations.Mojo;
@@ -28,7 +27,6 @@
 /**
  * Goal which stops all instances of {@link MiniAccumuloCluster} started with the start mojo.
  */
-@ThreadSafe
 @Mojo(name = "stop", defaultPhase = LifecyclePhase.POST_INTEGRATION_TEST,
     requiresDependencyResolution = ResolutionScope.TEST)
 public class StopMojo extends AbstractAccumuloMojo {