Resolve "High rate of config.lock file errors on Geo testbed"

What does this MR do?

Restores the use of a fixed remote name for Geo repository/wiki synchronization

Are there points in the code the reviewer needs to double check?

Reverts a change added in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3396

Why was this MR needed?

We run the sync process for every repository, and every time a repository is updated. We also limit the concurrency of these updates so we can't run two against the same repository in parallel.

If we use a temporary remote name, it has to be removed after use. This happens in a separate sidekiq job and seems to be causing problems on the Geo testbed.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #4693 (closed)