Deploy keys slow loading of project settings for 9.0

Overview

We combined repostiory settings in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8731 - This seems to have a performance impact.

Steps to reproduce

1. Visit https://gitlab.com/gitlab-org/gitlab-ce/settings/repository when logged in

Details

The median transaction time is 10 seconds.

• https://performance.gitlab.net/dashboard/db/rails-controllers?var-action=Projects::Settings::RepositoryController%23show&var-database=Production&from=now-24h&to=now

@smcgivern @jivanvl @stanhu