[TASK] Remove a set of skipped unit tests

This patch removes a series of unit tests from the
test sets that are often either skipped or flaky.

* There is little point in testing chmod() / chgrp()
  operations of low-level methods. That's a system thing
  we shouldn't test in detail.
* Some tests have been marked as "i'm mocking too much,
  make me a functional test". Most of these are oooold.
  Don't read it, delete it.
* Some phpunit @requires annotations have been broken
  since introduction and always resulted in "skip test".
  Remove those.

Change-Id: I82e04613c9b72712e279d0819ada8e073658968d
Resolves: #96301
Releases: main, 11.5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72567


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>