Make mojo dart controller depend on tonic and get building without wtf

tonic/dart_wrappable.h

Index: tonic/dart_wrappable.h
diff --git a/tonic/dart_wrappable.h b/tonic/dart_wrappable.h
index 13feb999cf4771cb0d5e6971e8254bd1e09d290e..94286013bbcdab4e57e22f8ae57be22598b3cc7b 100644
--- a/tonic/dart_wrappable.h
+++ b/tonic/dart_wrappable.h
@@ -123,17 +123,6 @@ struct DartConverter<
 };
 
 template<typename T>
-struct DartConverter<RefPtr<T>> {
-  static Dart_Handle ToDart(RefPtr<T> val) {
-    return DartConverter<T*>::ToDart(val.get());
-  }
-
-  static RefPtr<T> FromDart(Dart_Handle handle) {
-    return DartConverter<T*>::FromDart(handle);
-  }
-};
-
-template<typename T>
 inline T* GetReceiver(Dart_NativeArguments args) {
   intptr_t receiver;
   Dart_Handle result = Dart_GetNativeReceiver(args, &receiver);