[Utilities] Failed to deploy source jar due to duplicate maven-source-plugin effective

As two maven-source-plugin are effective*, it attempts to deploy the -source-x.x.x.jar twice when running `mvn deploy`. The second attempt always fails as it's already there.

-----
* When you run `mvn -Prelease-profile help:effective-pom`, you can see two maven-source-plugin effective in build/plugins section. This is because the root pom inherits:

  <parent>
    <groupId>org.onehippo.cms7</groupId>
    <artifactId>hippo-cms7-project</artifactId>
    <version>29</version>
  </parent>

where a different version of maven-source-plugin was already set.