This is a follow up to: #54202 

`thread_worktree_archive.rs` had its own
walk-up-and-remove-empty-parents pass that ran after archiving a Zed
managed git worktree. It duplicated logic that #54202 moved into
`Repository::remove_worktree` (which also adds remote support for this)

This PR deletes the dead code path and its associated tests.

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

Closes #ISSUE

Release Notes:

- N/A