message: Use static_cast to replace dynamic_cast to avoid needing RTTI
diff: @@ -229,8 +229,7 @@ private:
  template<typename T>
  typename T::ValueType & get(Symbol name) const {
  auto it = find(name, true);
  - T* child = dynamic_cast<T*>(it->get());
  - ONNX_ASSERT(child != nullptr);
  + T* child = static_cast<T*>(it->get());
  return child->value();
  }
  using AVPtr = AttributeValue::Ptr;
  