dns: remove nonexistant exports.ADNAME

This error code export was mistakingly introduced in a 2012 commit which
added more error codes. The correct export.BADNAME was added in
#3051.
Semver: Major
PR-URL: #3051Fixes: #3050
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

Author: silverwind

lib/dns.js

@@ -330,7 +330,6 @@ exports.NOTFOUND = 'ENOTFOUND';
 exports.NOTIMP='ENOTIMP';
 exports.REFUSED='EREFUSED';
 exports.BADQUERY='EBADQUERY';
-exports.ADNAME='EADNAME';
 exports.BADNAME='EBADNAME';
 exports.BADFAMILY='EBADFAMILY';
 exports.BADRESP='EBADRESP';