[TASK] Remove l10n_cat leftover

TCA property l10n_cat has been there since ever and nobody understood it.
The docs about it never said what it really does and the according arguments
from EditDocumentController were never used.
The patch removes l10n_cat and some left over handling in
EditDocumentController.
Do not confuse this l10n_cat related localizationMode text/media with the
localizationMode select/keep from inline: The inline part is not touched
by the patch.

Change-Id: Ia7b54bddabffcad3e38df76731d7fe9f6b8ff40f
Resolves: #80331
Releases: master
Reviewed-on: https://review.typo3.org/52086


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>