fix: properly destroy entities/material/etc in Gizmo on destruction, remove custom scene creation logic

thermion_dart/native/include/Gizmo.hpp

@@ -62,7 +62,6 @@ class Gizmo {
         Gizmo(Engine& engine, View *view, Scene *scene);
         ~Gizmo();
 
-        void destroy();
         Entity x() {
             return _entities[0];
         };