Clean up redirect routes that conflict with regular routes

What does this MR do?

Deletes any redirect routes that conflict with regular routes.

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

@yorickpeterse Would this query be too slow on GitLab.com? Should I do some kind of batching in a background migration?

Why was this MR needed?

This is needed because the conflicting redirect route scope had a bug in which we did not match case insensitively on Postgres. See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13357.

Screenshots (if relevant)

$ bundle exec rake db:migrate
== 20170823140235 DeleteConflictingRedirectRoutes: migrating ==================
-- Clean up redirect routes that conflict with regular routes.
   See initial bug fix: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13357
-- Deleted 3 redirect routes that were conflicting with routes.
== 20170823140235 DeleteConflictingRedirectRoutes: migrated (0.0015s) =========

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/36229