gitserver: Skip remote urls for private cloud default repos

Created by: ryanslade

We won't be able to use a remote URL for a private repo linked to a cloud default external service, so we should skip it. This can happen if a repo moves from being public to private while belonging to both a cloud default external service and another external service with a token that has access to the private repo.

I spotted this while looking into why we still have a bunch of repos that are consistently failing to update on cloud.

Test plan

We should see the number of repos in this gauge drop.