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/private/grid.h

@@ -17,10 +17,6 @@
 
 #include "wx/headerctrl.h"
 
-// Internally used (and hence intentionally not exported) event telling wxGrid
-// to hide the currently shown editor.
-wxDECLARE_EVENT( wxEVT_GRID_HIDE_EDITOR, wxCommandEvent );
-
 // ----------------------------------------------------------------------------
 // array classes
 // ----------------------------------------------------------------------------