Bring over the rails gem cleanup from omnibus
This matches the gem exclusions used in the GitLab Omnibus project https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/config/projects/gitlab.rb#L144
This matches the gem exclusions used in the GitLab Omnibus project https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/config/projects/gitlab.rb#L144