internal: remove vertexScale from unlit material and multiply by alpha

thermion_dart/native/include/material/UnlitMaterialProvider.hpp

@@ -36,7 +36,6 @@ public:
                                                        const char* extras = nullptr) override {
         auto instance = mUnlitMaterial->createInstance();
         instance->setParameter("baseColorIndex", -1);
-        instance->setParameter("vertexScale", 1.0f);
         instance->setParameter("uvScale", filament::math::float2 { 1.0f, 1.0f });
         return instance;
     }