[TASK] Remove special TSFE handling in FileCollector

The FileCollector is e.g. used for resolving
references in the FILES cObject. The check for
TSFE can be removed since the ->getFileReferences
functionality should be used at any time, as the
functionality always handles overlays depending
on the $referenceRecord given.

Resolves: #88859
Releases: master
Change-Id: I500421a12cced80e133b12a0caf6dcf289c6bd9a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61350


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>