Remove WIP/Draft regex title parsing

#228685 (comment 562984123)

This will complete Remove support for WIP prefix in merge requests

We will continue to allow users the workflow of changing the title to change status. When processing incoming changes to an MR (via MergeRequest::Update/CreateService) we will update the title by prepending/removing Draft: when the status changes) so that the title reflects the current draft status, however the Single Source of Truth (SSoT) about draft status should be the DB record, not the title.

• remove regex parsing of title
• remove regex as a Source Of Truth
• remove frontend regex parsing in favor of draft column status

Note that we may still need to support this regex in the backend, as we parse incoming commits for several triggers to change draft status