[BUGFIX] Move TCA modification of indexed_search 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: If5998b9c86bc5f7b106fd3f1c9213842b8ae242d
Resolves: #59468
Related: #59414
Releases: 6.3, 6.2
Reviewed-on: https://review.typo3.org/30652
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters