[BUGFIX] Clean up category references when a file is deleted

File are categorizable by default as of TYPO3 6.2
When a BE User deletes a file, associated categories
must be removed as well.

Change-Id: I82175bbd207e68590c20de8fd536bab0de001fe3
Releases: 6.2
Resolves: #55430
Reviewed-on: https://review.typo3.org/27124
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Andreas Wolf
Tested-by: Andreas Wolf