Commit c6f1761a deletes a stock item id. But this is also part of our API
and cannot be deleted. Yet since the associated label ("_Edit") is
identical to the one for GTK_STOCK_EDIT, we can simply redefine it
to "gtk-edit".
Ideally we would also add a deprecation warning when this macro is used,
but I can't find a good way to add deprecation on macros.