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/json.c b/src/json.c
index 450e1d6..e304709 100644
--- a/src/json.c
+++ b/src/json.c
@@ -24,7 +24,7 @@
 #include "parser_internal.h"
 
 #define JSON_PUSH_STATUS_RET(CTX, STATUS) \
-    LY_CHECK_RET(ly_set_add(&CTX->status, (void*)STATUS, LY_SET_OPT_USEASLIST, NULL))
+    LY_CHECK_RET(ly_set_add(&CTX->status, (void*)STATUS, 1, NULL))
 
 #define JSON_POP_STATUS_RET(CTX) \
     assert(CTX->status.count); CTX->status.count--;