Fix warning about non-virtual dtor in wxDataViewCtrlInternal.

This class doesn't need a virtual dtor but g++ warned about its absence
because it unnecessarily defined a virtual method. Just make this method
non-virtual to avoid the warning.

Closes #13395.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70125 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/dataview.cpp

@@ -279,7 +279,7 @@ public:
     // item can be deleted already in the model
     int GetIndexOf( const wxDataViewItem &parent, const wxDataViewItem &item );
 
-    virtual void OnInternalIdle();
+    void OnInternalIdle();
 
 protected:
     void InitTree();