FGS notifs are no longer upranked

With the relaxation of FGS visiblity rules in S, we
no longer need to boost FGS notifications to the
alerting section to ensure visibility on the lockscreen.

Test: atest HighPriorirtProviderTest
Bug: 182164793
Change-Id: I363c16708ab00bb3b2c4e3663bac2a6470a75274