Remove non overriding member

Author: Ortes

lib/src/web/web_unity_widget_controller.dart

@@ -35,9 +35,6 @@ class WebUnityWidgetController extends UnityWidgetController {
 
   MethodChannel? _channel;
 
-  @override
-  int get id => throw UnimplementedError("Platform does not support id");
-
   /// used for cancel the subscription
   StreamSubscription? _onUnityMessageSub,
       _onUnitySceneLoadedSub,