Remove email-level unsubscriptions #91
Description
Remove the unsubscriptions field on the Email model, and remove the EmailUnsubscriptionsListView and any links to this view (particularly the red "Unsubscriptions" button at the top of the Email update view). This view and the unsubscriptions field on the Email model have not been in use since subscription categories were implemented, and a one-time process was ran a while back to shift email unsubscriptions to their respective subscription categories.