Removes the Vercel v0 Provider, as the v0 API has been
depredated/removed (https://api.v0.dev/v1)

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- agent: Removed Vercel v0 provider as it has been deprecated by Vercel