[BUGFIX] Fix typo and improve backup of system settings

LC_MONETARY was saved to LC_TIME, this needs to be fixed.

Instead of using the constants as is, use the API function to save
and restore system settings.

Fixes: #45218
Releases: 4.5, 4.6, 4.7, 6.0, 6.1
Change-Id: I3c3c9d552d89d69c3689e60dc00e392067b98464
Reviewed-on: https://review.typo3.org/18073
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring