SDLPP: Don't save textures before render

Since textures should only be manipulated in the main thread (as well
as rendering), let programmers deal with ensuring the texture is
available during rendercopy

sdlpp/sdlpp_renderobject.cpp

@@ -119,7 +119,4 @@ void RenderObject::copyTo( std::shared_ptr< RenderObject > other ) {
     }
     other->colidedWith.clear();
 }
-void RenderObject::saveCurTexture() {
-    cur_texture = texture;
-}
 } // namespace SDLPP