Revert "Make UserSwitchObserver.onBeforeUserSwitching oneway but still blocking."

This reverts commit 65ee48d1eb9fe60039c2c461ca49f31ad180faef.

Reason for revert: Severe crashes "Timeout on dispatchOnBeforeUserSwitching" b/384838859, b/384848606

Change-Id: Ie6d5bbad202fd9b231de53c4aca6c7bfc9c41c6f
7 files changed