i18n: Fix message key duplication "coll-notitle_title"

- "coll-notitle_title" had been defined twice in Coll.i18n.php since over 6 years ago.
  One of them dropped on "JSON i18n" conversion (Iafb48504e7110b301919b1958356de6aeabbf2ac).
- Add a full-stop for consistency

Change-Id: I7be7d66205741635c9409556de9d7844b9cf2a17