Don't persist new night mode setting in car mode

Keep persist.sys.theme in sync with the primary user's
setting value UI_NIGHT_MODE

Test: manual
Fixes: 137174308
Change-Id: I8df67e0734b08bd82418e381d153d9012ecf99e4
(cherry picked from commit 47a775b6)
(cherry picked from commit 98288b3e)