Remove deprecated Devise setting
Remove deprecated Devise setting

This setting has had no effect since Devise 2.0, and was generating a
deprecation warning:
https://github.com/plataformatec/devise/wiki/How-To:-Upgrade-to-Devise-2.1

alphagov/signonotron2,alphagov/signonotron2,alphagov/signonotron2,alphagov/signonotron2