Don't derive wxAnimationImpl from wxObject

This is just unnecessary and having wxAnimation::m_refData->m_refData is
confusing, both in wxGTK version where it's not used and in the generic
one where it is, but can be replaced by more type-safe m_decoder.

include/wx/gtk/private/animate.h

@@ -64,7 +64,6 @@ private:
 
     typedef wxAnimationImpl base_type;
     wxDECLARE_NO_COPY_CLASS(wxAnimationGTKImpl);
-    wxDECLARE_DYNAMIC_CLASS(wxAnimationGTKImpl);
 };