Remove SET_FORCE_HIDING_CHANGED related logics.

As b/111362605 comment#15, remove SET_FORCE_HIDING_CHANGED &
mWallpaperForceHidingChanged related usages since it's no longer
used after reviewed.

Bug: 111362605
Test: atest ActivityManagerMultiDisplayTests
Test: atest ActivityManagerTransitionSelectionTests
Test: atest WindowSurfacePlacerTest RootWindowContainerTests AppTransitionTests
Change-Id: I2c87bfed2791ddd8b733ca08be0e1c965d9ee9f7