Add spec for deletion of authorized OAuth2 application

CHANGELOG

app/controllers/application_controller.rb

app/controllers/oauth/applications_controller.rb

app/models/oauth_access_token.rb

lib/gitlab/current_settings.rb

lib/gitlab/gon_helper.rb

spec/factories/oauth_access_tokens.rb

spec/factories/oauth_applications.rb

spec/factories/users.rb

spec/features/profiles/oauth_applications_spec.rb