Disables https://github.com/zed-industries/zed/pull/26146 until a better
way to add diagnostics is found.
Overall, the PR had made changes that are worth keeping instead of
reverting, such as finally extracting out r-a's language server logic
into an `_ext.rs` file.
Release Notes:
- N/A
Kirill Bulatov
690f26cf8b