Woohoo! I read about `let!` yesterday, but by that stage my brain was too addled to make sense of it so I thought it did something different. Removing redundant nonsense FTW.

BTW, I used `should be_persisted` there in the first place because I saw it in [organisations_controller_spec](https://github.com/alphagov/transition/blob/master/spec/controllers/organisation_controller_spec.rb#L10-11) - is it intended to do something different there?