Revert "Exclude maven-plugin as transitive dependency of promoted-builds"

This reverts commit 5a4f072.

Fails a test in the plugin compatibility tester.  Needs more
investigation before it is allowed in the master branch.

Author: MarkEWaite

pom.xml

@@ -251,10 +251,6 @@
           <groupId>org.sonatype.sisu</groupId>
           <artifactId>sisu-guava</artifactId>
         </exclusion>
-        <exclusion>
-          <groupId>org.jenkins-ci.main</groupId>
-          <artifactId>maven-plugin</artifactId>
-        </exclusion>
       </exclusions>
     </dependency>
     <dependency>