[TASK] Move TCA modification 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.

Releases: 2.0.0
Change-Id: I033db880e508f4feace3cd9b85ced75b9474097d
Reviewed-on: https://review.typo3.org/31584
Reviewed-by: Alexander Schnitzler <typo3@alexanderschnitzler.de>
Tested-by: Alexander Schnitzler <typo3@alexanderschnitzler.de>