Don't store header height in generic wxListCtrl member variable.

This is simply unnecessary and resulted in a crash in wxDFB because the window
was used for this variable initialization before being created.

Closes #11711.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63638 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/listctrl.h

@@ -212,7 +212,6 @@ public:
                          m_ownsImageListState;
     wxListHeaderWindow  *m_headerWin;
     wxListMainWindow    *m_mainWin;
-    wxCoord              m_headerHeight;
 
 protected:
     virtual bool DoPopupMenu( wxMenu *menu, int x, int y );