[BUGFIX] Use correct values in settings InstallTool

Currently, the InstallTool will use the global TYPO3_CONF_VARS for the
settings form. In backend context, this contains merged TypoScript,
which shouldn't be added to LocalConfiguration.php.

Resolves: #82399
Releases: master
Change-Id: I0aabbde5c8fb8574fe30422fa687849271a3d618
Reviewed-on: https://review.typo3.org/54049


Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>