Followup 5963c03643 and
6be4ef59fa
This migration was causing issues on deploy for some sites that
had user fields required to be filled in on signup. The Site#user_fields
cache was getting poisoned, and the `field_type` for all fields
was ending up as `null`, making it impossible to fill
them out in a form.
This commit rectifies the issue by doing the column rename/swap
in the initial migration and _only_ dropping columns in the
post migration, since this messes with the AR cache.
79344fe212