UPBGE: Fix scene replacement.

The commit f62dca6 introduced a remove of the replaced
scene in the scene list, this call is unnecessary as
EXP_ListValue::SetValue is swapping the values.
The drawback of RemoveValue was to reduce the size of the
container by actually erasing the item.

This is fixed by not removing the scene but only replacing
its pointer.

Fix issue: #819.

source/gameengine/Ketsji/KX_KetsjiEngine.cpp

@@ -1397,7 +1397,6 @@ void KX_KetsjiEngine::ReplaceScheduledScenes()
 					Scene *blScene = m_converter->GetBlenderSceneForName(newscenename);
 					if (blScene) {
 						DestructScene(scene);
-						m_scenes->RemoveValue(scene);
 
 						KX_Scene *tmpscene = CreateScene(blScene);
 						ConvertScene(tmpscene);