Idk if this used to be different or what, but it looks like the current
behavior is: if you delete a closet list, it'll leave the hangers
present, but Classic DTI would not show them anywhere; but Impress 2020
(until recently) would crash about it.
Now, we use `dependent: :destroy` to delete the hangers when you delete
the list (which I think makes sense, and is different than what I
decided in the past but that's ok, and is what the current behavior
*looks* like to people!), and we add a migration that deletes orphaned
hangers.
The migration also outputs the deleted hangers as JSON, for us to hold
onto in case we made a mistake! I'm also backing up the database in
advance of running this migration, just in case we gotta roll back HARD!
