Removed isUserStoppingOrShuttingDownLocked

It was causing issues when user state was removed (or user was never
started).
Replaced it with isUserRunningLocked which returns false if user state
is null/shutdown or stopping.

Test: manual - create/switch to/from guest user
Bug: 64319208
Change-Id: I88dae7111692e760b10cd7db13d5cd17dae2f2cb