Move event generation code for multiple selection mode to common code

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53715 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/listbox.h

@@ -97,9 +97,6 @@ public:
 
     void GtkDisableEvents();
     void GtkEnableEvents();
-    
-    wxArrayInt m_oldSelection;
-    void GtkUpdateOldSelection();
 
 protected:
     virtual void DoClear();