[BUGFIX] Move TCA modification of saltedpasswords 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: I328cbcb718ee33beec19379ea6047a18cdc370b0
Resolves: #59704
Related: #59414
Releases: 6.3, 6.2
Reviewed-on: https://review.typo3.org/31351
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters