Remove support for WIP prefix in merge requests

Problem

WIP limits are being added to issue boards #11403 (closed) which creates a naming collision with WIP (Work In Progress) merge requests.

Furthermore, WIP merge requests are frequently used to mean "this MR is a draft, please don't merge" even though they are complete and ready for review.

#32692 (closed) introduced the ability to use either draft or wip prefixes, however, we want to deprecate and remove wip

Proposal

Remove support for wip as a prefix for MRs and use draft as the only term to indicate a work in progress.

Backend

• Remove WIP quick actions
• Drop support for WIP: and variations of this title prefix
• Replace usage of WIP in the API
• GraphQL API updates have a separate issue: #321892 (closed)

Frontend

• Remove the quick toggle on the MR Form to add/remove WIP[:] prefix