Aye, there may be multiple tokens issued to the same origin for the same user (see [this thread](https://github.com/mozilla/openbadges/pull/664#discussion_r3232427)) and the pre-existing `destroy` method can only destroy individual instances. We could technically do a `find` for all tokens matching the criteria and then use the `async` module to `destroy` them all, but that feels kind of weird and non-atomic...