Remove wxHeaderColumn::SetAsSortKey() and only use SetSortOrder().

The two member functions, SetAsSortKey() and SetSortOrder(), were doing almost
the same thing but differently and the former was only used in the generic
wxDataViewCtrl implementation and not implemented in the native GTK/OS X one.

Remove SetAsSortKey() entirely and only keep UnsetAsSortKey() which is still
needed by generic/MSW wxDataViewCtrl. But only SetSortOrder() should now be
called to indicate that the column is used for sorting.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69174 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/dataview.cpp

@@ -3286,14 +3286,6 @@ bool wxDataViewColumn::IsSortable() const
     return gtk_tree_view_column_get_clickable( column );
 }
 
-void wxDataViewColumn::SetAsSortKey( bool WXUNUSED(sort) )
-{
-    // it might not make sense to have this function in wxHeaderColumn at
-    // all in fact, changing of the sort order should only be done using the
-    // associated control API
-    wxFAIL_MSG( "not implemented" );
-}
-
 bool wxDataViewColumn::IsSortKey() const
 {
     GtkTreeViewColumn *column = GTK_TREE_VIEW_COLUMN(m_column);