This is a partial revert of #5893. The problem is that if we drop these tables
in the same release as removing the code that writes to them, it prevents users
users from being able to roll back to a previous release.
So let's leave the tables in place for now, and remember to drop them in a
subsequent release.
(Note that these tables haven't been *read* for *years*, so any missing rows
resulting from a temporary upgrade to vNext won't cause a problem.)
