Remove use of locks (5/n)

Now that all state changes happen on the same thread, we don't need
locks anymore.

TODO: fix indentation and method names suffixed with "Locked".

Bug: 145335013
Test: atest CtsRollbackManagerHostTestCases
Test: atest RollbackTest
Test: atest StagedRollbackTest

Change-Id: Ia8e73bea07d0688baef66e95185e0830a9e08cf3