Remove subtitle field from item fields

Co-authored-by: openhands <openhands@all-hands.dev>

Author: openhands-agent

lib/fields.js

@@ -36,7 +36,6 @@ fields.item = [
   ['dc:source', 'source'],
   ['dc:title', 'title'],
   'title',
-  'subtitle',
   'link',
   'pubDate',
   'author',