Temporarily revert git panel diff editor feature (#22733)

The existing code was causing us to constantly re-scan files when
anything changed in the project. Temporarily revert this as we're about
to rework this entire UI with the new primitives.

follow up to https://github.com/zed-industries/zed/pull/22329

Release Notes:

- N/A

---------

Co-authored-by: Cole <cole@zed.dev>

crates/project_panel/src/project_panel.rs

@@ -311,7 +311,7 @@ impl ProjectPanel {
                     this.update_visible_entries(None, cx);
                     cx.notify();
                 }
-                project::Event::GitRepositoryUpdated
+                project::Event::WorktreeUpdatedGitRepositories(_)
                 | project::Event::WorktreeUpdatedEntries(_, _)
                 | project::Event::WorktreeAdded(_)
                 | project::Event::WorktreeOrderChanged => {