[TASK] Deprecate TypoScriptFrontendController->page_cache_reg1

Property page_cache_reg1 is a poor man limited way to manipulate
page cache tagging. It has been of very little use and is
deprecated now.

The usage in indexed_search (which always only added the default "0"
to database) is dropped along the way.

Change-Id: I9ea129fc6d20adb7a35a719f3d9d630aa663952f
Resolves: #83905
Releases: master
Reviewed-on: https://review.typo3.org/55723


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>