PARQUET-1607: Remove duplicate maven-enforcer-plugin (#658)

* PARQUET-1607: Remove duplicate maven-enforcer-plugin

[WARNING] Some problems were encountered while building the effective model for org.apache.parquet:parquet-cascading3:jar:1.12.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.(groupId:artifactId)' must be unique but found duplicate declaration of plugin org.apache.maven.plugins:maven-enforcer-plugin @ org.apache.parquet:parquet-cascading3:[unknown-version], /home/travis/build/Fokko/parquet-mr/parquet-cascading3/pom.xml, line 167, column 15
[WARNING]

* Add exclusion for slf4j-log4j12
diff --git a/parquet-cascading3/pom.xml b/parquet-cascading3/pom.xml
index 4e5c4ad..d77d7f9 100644
--- a/parquet-cascading3/pom.xml
+++ b/parquet-cascading3/pom.xml
@@ -65,6 +65,12 @@
       <artifactId>hadoop-client</artifactId>
       <version>${hadoop.version}</version>
       <scope>provided</scope>
+      <exclusions>
+        <exclusion>
+          <groupId>org.slf4j</groupId>
+          <artifactId>slf4j-log4j12</artifactId>
+        </exclusion>
+      </exclusions>
     </dependency>
     <dependency>
       <groupId>org.apache.thrift</groupId>
@@ -101,24 +107,6 @@
 
   <build>
     <plugins>
-        <!-- TEMPORARY UNTIL AFTER previous.version &gt;= 1.8.2
-
-        (enforcer checks against the API in 1.7.0, this module did not exist back then, therefore it can't succeed)
-        -->
-      <plugin>
-        <artifactId>maven-enforcer-plugin</artifactId>
-        <executions>
-          <execution>
-            <phase>none</phase>
-          </execution>
-        </executions>
-        <configuration>
-          <skip>true</skip>
-        </configuration>
-      </plugin>
-
-        <!-- /TEMPORARY -->
-
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>build-helper-maven-plugin</artifactId>