E2E test: enable fork mr test in prod

What does this MR do?

De-quarantine merge from fork E2E test in production. Previously it was failing due to #372258 (closed) , this issue still exists but this MR was merged which remove groups that were building up against gitlab-qa-user-1. Additionally groups have been deleted in prod to reduce the number of groups from 205 to 5.

Also includes renaming test.

bundle exec rspec qa/specs/features/browser_ui/3_create/merge_request/merge_merge_request_from_fork_spec.rb