Lower log level for message about removing clients from the registry

Servers stopped with `:lsp-stop` will show this message when the server
exits. If the client isn't in the registry there isn't any work to do
to remove it so this branch is benign.

helix-lsp/src/lib.rs

@@ -675,7 +675,7 @@ impl Registry {
 
     pub fn remove_by_id(&mut self, id: LanguageServerId) {
         let Some(client) = self.inner.remove(id) else {
-            log::error!("client was already removed");
+            log::debug!("client was already removed");
             return;
         };
         self.file_event_handler.remove_client(id);