Replace wxEVT_GRID_HIDE_EDITOR usage with CallAfter

This simplifies the code by removing the need for a special event,
and also means the combox popup handler is no longer needed to reset
the inSetFocus flag for the closing handler.

include/wx/generic/grid.h

@@ -2827,7 +2827,6 @@ protected:
     void OnKeyDown( wxKeyEvent& );
     void OnKeyUp( wxKeyEvent& );
     void OnChar( wxKeyEvent& );
-    void OnHideEditor( wxCommandEvent& );
 
 
     bool SetCurrentCell( const wxGridCellCoords& coords );