Remove 1.6 JVM compliance: getting the 1.7 from top pom.xml

The top-level pom.xml already defines Java 1.7 as the source
and binary compliance level: this change aligns the plugin to the top
level setting.

Change-Id: I819c830f7eb5d9fc509183ea961cb192e6627786
diff --git a/github-plugin/pom.xml b/github-plugin/pom.xml
index 4d62828..a7f56d6 100644
--- a/github-plugin/pom.xml
+++ b/github-plugin/pom.xml
@@ -86,17 +86,6 @@
           </execution>
         </executions>
       </plugin>
-
-      <plugin>
-        <groupId>org.apache.maven.plugins</groupId>
-        <artifactId>maven-compiler-plugin</artifactId>
-        <version>2.3.2</version>
-        <configuration>
-          <source>1.6</source>
-          <target>1.6</target>
-          <encoding>UTF-8</encoding>
-        </configuration>
-      </plugin>
     </plugins>
   </build>