Clean up deferDisplayUpdates flag

The flag was enabled since previous release.

PhysicalDisplaySwitchTransitionLauncher is only used by
ImmediateDisplayUpdater which was replaced by DeferredDisplayUpdater.
So the related classes can be removed.

Bug: 259220649
Flag: EXEMPT remove dead code for launched flag
Test: DisplayContentDeferredUpdateTests
Change-Id: I57478ca252f32b714f7d4a2e3d2587043432192e