js: Remove unused catch bindings

Optional catch bindings have been supported for quite a while now,
so we can treat unused error bindings in catch statements like any
other unused variable.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3684>

js/ui/main.js

@@ -156,7 +156,7 @@ export async function start() {
             // toString() can throw
             if (msg)
                 args.unshift(`${msg}:`);
-        } catch (e) {}
+        } catch {}
 
         console.error(...args);
     };