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/animate.h

@@ -37,10 +37,11 @@ enum wxAnimationImplType
     wxANIMATION_IMPL_TYPE_GENERIC
 };
 
-class WXDLLIMPEXP_CORE wxAnimationImpl : public wxObject, public wxRefCounter
+class WXDLLIMPEXP_CORE wxAnimationImpl : public wxRefCounter
 {
 public:
     wxAnimationImpl() {}
+    virtual ~wxAnimationImpl() {}
 
     virtual wxAnimationImplType GetImplType() = 0;