Fixes T12628. After later changes to PhabricatorFile, this migration no longer runs if you upgrade through it to a recent HEAD while your data has some room images.
Since this isn't critical and has been available for ~6 months, I just nuked it as a first pass. I can find a more careful approach which lets us continue to run this migration instead if you're hesitant to skip this step, although it may be a little involved.
In 95% of cases we avoid this by updating the storage table as it existed at the time the migraiton ran, but Files are much too complicated for that to be realistic.