Fix ruff server hanging after Neovim closes (#11291)

## Summary

A follow-up to https://github.com/astral-sh/ruff/pull/11222. `ruff
server` stalls during shutdown with Neovim because after it receives an
exit notification and closes the I/O thread, it attempts to log a
success message to `stderr`. Removing this log statement fixes this
issue.

## Test Plan

Track the instances of `ruff` in the OS task manager as you open and
close Neovim. A new instance should appear when Neovim starts and it
should disappear once Neovim is closed.

crates/ruff_server/src/server.rs

@@ -114,9 +114,6 @@ impl Server {
                 self.worker_threads,
             )?;
             self.connection.close()?;
-            // Note: when we start routing tracing through the LSP,
-            // this should be replaced with a log directly to `stderr`.
-            tracing::info!("Server has shut down successfully");
             Ok(())
         })?
         .join()