Revert "chore(project): bump django-storages to 1.14.4" (#11569)

Reverts #11560

New version of django-storages introduced behavior that breaks
`exists()` when `allow_overwrite` is True. This is going to be reverted,
but there's no release with the revert yet. See this PR for more info:
jschneier/django-storages#1422

For now we can revert the library updates from yesterday (esp bc they
didn't fix the problem we were trying to fix at the time), and when
django-storages gets an update we can try again.