Lauren, here's a fairly simple but wide-ranging review for you. It just removes a lot of temporary backwards compability code that isn't needed anymore. It touches five packages, and you can find the changesets in the GitHub PRs linked from the issue page.
Note that this is just one part of a larger issue (
DM-1766), and I plan to hold off on merging it (even though I think it should be safe to merge) until the other subtasks are done and reviewed as well (but I'll ask other people to review the other things).