[TASK] Remove unused local variables

Add test coverage for GeneralUtility::getFilesInDir with sorting by
mtime.

Resolves: #103817
Releases: main
Change-Id: I298f63fef0369cf2fefd0876628ca55a152947c9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84190


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>