style: remove unused payload

src/routes/+layout.svelte

@@ -19,7 +19,7 @@
         });
         const spacesChannel = supabase
             .channel("study_space_updates")
-            .on("broadcast", { event: "study_space_updated" }, (payload) => {
+            .on("broadcast", { event: "study_space_updated" }, () => {
                 invalidate("db:study_spaces");
             })
             .subscribe();