[BUGFIX] Move TCA modification of EXT:cms to TCA/Overrides.

TCA manipulation code must no longer reside in ext_tables.php, but
moved to Configuration/TCA/Overrides/<tablename>.php. Leftovers
in ext_tables might disturb loading order of TCA changes and spoil
proper caching.

Change-Id: Idb1be39c754d5566e52623103477b94887077cdb
Resolves: #59463
Related: #59414
Releases: 6.3, 6.2
Reviewed-on: https://review.typo3.org/30648
Reviewed-by: Susanne Moog
Tested-by: Susanne Moog
Reviewed-by: Sebastian Fischer
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn