Revert "OMS: replace OMSImpl.OverlayChangeListener with return v..."

Revert submission 1507500-oms-transactional-api

Reason for revert: b/177065099
Reverted Changes:
Ie5344c53d:OMS: add tests for the OMS transactional API
I8f54e1532:Push OverlayDeviceTests onto /system
I63df58510:OMS: add transactional API
Idacc0c67e:OverlayDeviceTests: add missing TEST_MAPPING
I2452f789a:OMS: block until settings are persisted
If58d5e9dd:OMS: replace OMSImpl.OverlayChangeListener with re...

Change-Id: I9e7d79d767b2474ecea78907e98c86b244055bac