[BUGFIX] Verify folder access for file mounts of BE users

The current implementation does not allow non-admins backend
users to import files as the folder access always returns false
due to the empty $mounts variable inside BasicFileFunc.

As FAL does the permission checks automatically, the logic
from BasicFileFunc is not needed anymore, and can be
accessed directly.

Resolves: #75331
Releases: master
Change-Id: I0211286cc6ae939229a0d7eb45adc89d1600d635
Reviewed-on: https://review.typo3.org/47454


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>