collab: Remove `/contributors` endpoints (#46418)

This PR removes the `GET /contributors` and `POST /contributors`
endpoints.

The former was not in use anywhere, and the latter has been moved to
Cloud.

Part of CLO-33.

Release Notes:

- N/A
2dfb13c4e5Marshall Bowers committed on 1/9/2026, 4:46:23 AM· committed by GitHubparentfeb04ff
6 files changedLine totals unavailable