Remove preferKeepClearAreaForFocusDelay, turn it into a flag

TV PiP repositioning in response to keep clear area changes will be
debounced in SystemUI, so the client side delay in setting a keep clear
area with focus becomes obsolete.
Instead the config is turned into a flag for whether focused views
should automatically be marked as keep clear areas.

Bug: 231309309
Test: atest KeepClearRectsTests
Change-Id: I0ac61e671bb75e22a95b400c9bd8d84004379e43
Merged-In: I0ac61e671bb75e22a95b400c9bd8d84004379e43