agent: Remove experimental plan and title agent tools (#58824)

Neither really panned out, removing for now.

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)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A
f8226fd1ebBen Brandt committed on 6/8/2026, 11:39:49 AM· committed by GitHubparentea50042
12 files changedLine totals unavailable