[BUGFIX] Make non-visible l10n_parent fields of type group

The l10n_parent fields of sys_file_metadata and sys_file_reference are
never shown anywhere. Having them as type 'select' in the TCA causes the
FormEngine to try loading all possible parent value, which can be
thousands or more. This degrades backend performance towards unusable.

Changing the TCA definition to 'group' mitigates the issue easily as no
lookup list has to be created/loaded.

Resolves: #92863
Releases: master, 10.4
Change-Id: Ibf76ac51f6d79a69fdc19bfe1993bcb6c97de233
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66671


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>