Add wxListCtrl::EnableAlternateRowColours() and SetAlternateRowColour().

Add methods to simply enable alternative row background colours in wxListCtrl.

Closes #14618.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73239 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/listctrl.h

@@ -229,9 +229,6 @@ protected:
     // return the icon for the given item and column.
     virtual int OnGetItemColumnImage(long item, long column) const;
 
-    // return the attribute for the item (may return NULL if none)
-    virtual wxListItemAttr *OnGetItemAttr(long item) const;
-
     // it calls our OnGetXXX() functions
     friend class WXDLLIMPEXP_FWD_CORE wxListMainWindow;