Change visibility of some classes/methods (6/n)

They don't have to be public since they are used internally inside
RollbackManager.

Bug: 150347230
Test: atest RollbackUnitTest RollbackStoreTest AppDataRollbackHelperTest
Test: atest RollbackTest StagedRollbackTest
Change-Id: I53dc2a613519a78d18ed7597c45af2ea7d5e774d