Fix some Installer methods (4/n)

1. snapshotAppData now returns a boolean
2. destroyAppDataSnapshot now doesn't take ceSnapshotInode

As we clean up the code that deletes snapshots by inode, the return
value and the parameter are no longer used.

Bug: 154897348
Test: atest RollbackUnitTest RollbackStoreTest AppDataRollbackHelperTest
Change-Id: I3d8740ccec7da732db80d524d9c17e38d5d9621d