[WFCORE-213] :  Clean unreferenced items from the content repository

We are using ContentReference to track contents in the content repository.
Se are tracking references to overlays.
Trying to use server group definition for domain mode.
Simplifying ContentReference
WFCORE-211: Fixing overzealous cleaning of HC content.
WFCORE-178: ContentRepositoryImpl should not call File.deleteOnExit

Jira: https://issues.jboss.org/browse/WFCORE-213
and https://issues.jboss.org/browse/WFCORE-211
and https://issues.jboss.org/browse/WFCORE-178
Please double-check, as it's a long chain of method calls, but I believe contentRepository will never be null.

In the old logic, fileRepository was never null, and that was ok, even if the slave wasn't backup-dc, because if the deployment is removed from the model, it is safe to remove the file from the repo (and it won't fail if the file doesn't exist.)

I think the same logic applies here -- regardless of what the slave is doing, it is safe to call contentRepository.removeContent.

Given all that, the contentRepository will never be null, and the fileRepository will never be used and can be removed from the class.

This could use a comment as it took me a bit of poking around and thinking to figure out why the old logic worked the way it did and therefor your new logic with the contentRepository is ok.