[CS] Remove CentralSurfaces#isOccluded.

Move clients of this method to ask KeyguardStateController directly for
the occluded status.

Bug: 277764509
Test: verified via logging that clients are still getting the correct
occluded status

Change-Id: Ibd920f6ab6236d77f4fedef6e366c83a4a40295c
5 files changed