Update the Zendesk ticket content for

`check_if_letters_still_in_created`

The message to Zendesk includes a list of notification ids, this isn't
really necessary and is included in the run book. Creation of the
Zendesk ticket can fail if the message is too long, removing the list of
ids can prevent that from happening.

app/celery/scheduled_tasks.py

@@ -226,13 +226,10 @@ def check_if_letters_still_in_created():
     letters = dao_old_letters_with_created_status()
 
     if len(letters) > 0:
-        letter_ids = [str(letter.id) for letter in letters]
-
         msg = "{} letters were created before 17.30 yesterday and still have 'created' status. " \
             "Follow runbook to resolve: " \
             "https://github.com/alphagov/notifications-manuals/wiki/Support-Runbook" \
-            "#deal-with-Letters-still-in-created. " \
-            "Notifications: {}".format(len(letters), letter_ids)
+            "#deal-with-Letters-still-in-created.".format(len(letters))
 
         current_app.logger.warning(msg)