This commit fixes the following issue:
* User creates a post
* Akismet or some other thing like requiring posts to be approved puts
the post in the review queue, deleting it
* Admin approves the post
* Email is never sent to mailing list mode subscribers
We intentionally do not enqueue this for every single post when
recovering a topic (i.e. recovering the first post) since the topics
could have a lot of posts with emails already sent, and we don't want
to clog sidekiq with thousands of notify jobs.