Remove admin_uri from gitlab.yml

Created by: jouve

We must give options for git twice in git_host section of gitlab.yml :

• for the gitolite-admin repo, we have admin_uri (Gitlab.config.gitolite_admin_uri)
• for all other repo, we have git_user, host and port (Gitlab.config.ssh_path)

This is confusing and redondant because admin_uri is easily calculated with Gitlab.config.ssh_path + "gitolite-admin"