Clean up flag usage in KeyguardStateCallbackInteractor

When KeyguardWmStateRefactor is disabled, this means that
SceneContainerFlag should also be disabled. Thus, we can clean up the
extra logic in KeyguardStateCallbackInteractor.

Bug: None
Test: KeyguardStateCallbackInteractorTest
Flag: EXEMPT clean up
Change-Id: I58cc40ca2a0e3cacc42f5889ad99690679dc8aac