Similar to ChangeUpdate in Ib163d209, most of the VersionedMetaData
methods weren't actually being used, and using them accidentally would
lead to unexpected results.
Copy the few methods we do need into AbstractChangeNotes. This is not
a complete rethinking of the AbstractChangeNotes API, just a minimal
code change. But it does open up that possibility later if we want it.
Change-Id: I1e56a80cc8daa90fa7ac0dc985d31f22123c0a55
976c714dd8