Ensure ordering in transition processing

withContext does not provide that guarantee. Use a Mutex to
ensure that transitions do not run out of order. This was
first reported during a DOZING->LOCKSCREEN->OCCLUDED transition
on double-tap power press but was processed as
DOZING->OCCLUDED->LOCKSCREEN due to withContext.

Also, remove an unnecessary audit log

Fixes: 340041643
Test: atest KeyguardTransitionScenariosTest
KeyguardTransitionRepositoryTest
Flag: None
Change-Id: I0d4d35634f140658b384d06a16adbc6fca15aab0

Change-Id: I75ccc43c0d3b3775443486b62a312f82953cca3e