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/status/keyboard.js

@@ -226,7 +226,7 @@ class InputSourceSystemSettings extends InputSourceSettings {
                 new GLib.Variant('(s)', [this._BUS_IFACE]),
                 null, Gio.DBusCallFlags.NONE, -1, null);
             [props] = result.deepUnpack();
-        } catch (e) {
+        } catch {
             log(`Could not get properties from ${this._BUS_NAME}`);
             return;
         }