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/unlockDialog.js

@@ -499,7 +499,7 @@ export const UnlockDialog = GObject.registerClass({
             this._gdmClient.set_enabled_extensions([
                 Gdm.UserVerifierChoiceList.interface_info().name,
             ]);
-        } catch (e) {
+        } catch {
         }
 
         this._adjustment = new St.Adjustment({