Cleanup Scene include / forward declaration.

Source/Urho3D/Scene/Scene.cpp

@@ -42,7 +42,6 @@
 #include "../Scene/SplinePath.h"
 #include "../Scene/UnknownComponent.h"
 #include "../Scene/ValueAnimation.h"
-#include "../Graphics/Renderer.h"
 
 #include "../DebugNew.h"
 

Source/Urho3D/Scene/Scene.h

@@ -34,7 +34,6 @@ namespace Urho3D
 
 class File;
 class PackageFile;
-class Viewport;
 
 static const unsigned FIRST_REPLICATED_ID = 0x1;
 static const unsigned LAST_REPLICATED_ID = 0xffffff;