[BUGFIX] Access to sys_files is incompatible to fe_access checks

The system extension filemetadata adds access restriction fields
for selecting frontend user groups as known from tt_content or
pages. Behind the scenes of the TCEform this relation is stored
in a MM table which is incompatible to the usual access checks.

In addition a opposite relation is added to fe_groups which
queries all files to show in a selector.

This change removes the MM table and reconfigures the fe_groups
field in the same way as it is done for tt_content and pages.

Resolves: #54236
Resolves: #54237
Releases: 6.2
Change-Id: I8a05073dee9e57e48335e1fe2a3917313563ac7d
Reviewed-on: https://review.typo3.org/25987
Reviewed-by: Markus Klein
Reviewed-by: Stefan Froemken
Tested-by: Stefan Froemken
Reviewed-by: Frans Saris
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter