Suppress group changes in group pruning

If they are suppressed by the visual stability manager
Also fix VSM logic - actually remove the notifications from its parent
when we're suppressing its new group

Test: atest ShadeListBuilderTest
Test: atest VisualStabilityCoordinatorTest
Test: manual, atest SystemUITest
Change-Id: I4ca9905a2347173a3871de43c11df3a2a1da623b