The backwards compatible distlock was a distlock taken by sharding catalog commands on a database's name, plus "-movePrimary."

It was taken by the sharding catalog commands in v3.6, because prior to v3.6, movePrimary had a bug that it took the database distlock with this "-movePrimary" suffix, rather than just the database's name.

Now that we don't need to support backwards compatibility with <v3.6, we can remove the places where we take this backwards compatible distlock.