Remove ovl_used, it is no longer needed
	* cp-tree.h (OVL_USED_P): Delete.
	(lookup_keep): Delete.
	* friend.c (add_friend): Don't call it.
	* parser.c (lookup_literal_operator): Likewise.
	(cp_parser_primary_expression): Likewise.
	* semantics.c (perform_koenig_lookup): Likewise.
	* pt.c (tsubst_copy <OVERLOAD>): Don't assert OVL_USED_P.
	* tree.c (ovl_copy): Delete.
	(ovl_insert): Remove OVL_USED_P checks.
	(ovl_iterator::reveal_node): Likewise.
	(ovl_iterator::remove__node): Likewise.
	(ovl_used, lookup_keep): Delete.

From-SVN: r266212