[BUGFIX] Move TCA modification of EXT:t3editor 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: I1f92a7b536ffb19d30bb580ea30452fc488cd0f6
Resolves: #59705
Related: #59414
Releases: 6.3, 6.2
Reviewed-on: https://review.typo3.org/30944
Reviewed-by: Sebastian Fischer
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn