set CHANGE replace LY_SET_OPT_USEASLIST by a single flag in ly_set_add()

There was just a single option and the ly_set API is quite stable for a
long time, so there will be hardly any new option. So instead of an
option bitmask with a single value, make the ly_set_add() parameter only
a single flag to switch off checking (and ignoring) items already
present in the set.
diff --git a/src/parser.c b/src/parser.c
index 6cc0824..36c7928 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -415,7 +415,7 @@
     LY_CHECK_RET(lyd_create_term(schema, value, value_len, dynamic, format, prefix_data, hints, &incomplete, node));
 
     if (incomplete && !(lydctx->parse_options & LYD_PARSE_ONLY)) {
-        LY_CHECK_RET(ly_set_add(&lydctx->unres_node_type, *node, LY_SET_OPT_USEASLIST, NULL));
+        LY_CHECK_RET(ly_set_add(&lydctx->unres_node_type, *node, 1, NULL));
     }
     return LY_SUCCESS;
 }
@@ -431,7 +431,7 @@
             hints, &incomplete));
 
     if (incomplete && !(lydctx->parse_options & LYD_PARSE_ONLY)) {
-        LY_CHECK_RET(ly_set_add(&lydctx->unres_meta_type, *meta, LY_SET_OPT_USEASLIST, NULL));
+        LY_CHECK_RET(ly_set_add(&lydctx->unres_meta_type, *meta, 1, NULL));
     }
     return LY_SUCCESS;
 }