Remove expectation data from mongodb

www.agileplannerapp.com/boards/173808/cards/8852

an [earlier story](www.agileplannerapp.com/boards/173808/cards/8707) migrated expectations to a govspeak field `need_to_know`, and this got deployed to production. so we no longer need this data in mongodb.
Fair point, should have been a collection drop in the first place. Thanks for pointing out!