docs: Clean up old plan document (#51926)

## Context

Shouldn't have been committed in the first place.

## Self-Review Checklist

<!-- Check before requesting review: -->
- [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
6758ac3590Ben Brandt committed on 3/19/2026, 11:54:45 AM· committed by GitHubparent99d51a4
1 file changedLine totals unavailable