Remove flag for keyguard remote animations [2/n]

Removed persist.wm.enable_remote_keyguard_animation system property, and
constants in WindowManagerService derived from the property.

Some variables become constant after removal of the system property, so
they are also removed and the logic around them is simplified.

Bug: 242833285
Test: Pass existing tests.
Change-Id: Ib103172b75429bf923515eb7a45c055b12557817