[BUGFIX] Fix reference count when ref_table is sys_file

When ref_table is sys_file the references to sys_file_metadata
should be excluded. Otherwise the deletion of sys_file records
can throw a message that there still is a reference but that is
not listed in the filelist column "Ref".

Resolves: #78368
Releases: master,7.6,6.2
Change-Id: I8cbfd93f53e1c3bf78e1f5a23f84ccae731da3ff
Reviewed-on: https://review.typo3.org/50299


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Robert van Kammen <rvkammen@hotmail.com>
Tested-by: Robert van Kammen <rvkammen@hotmail.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>