rails/rails — pull request #17929 by sergey-alekseev (2014-12-05 12:49:06+00:00)
Title: remove unused `#await_sent`

Seems it was unused from the start:
https://github.com/rails/rails/commit/3df07d093a1e4207caa63fd2e3b67599211f5800#diff-0b53645cdb23933ef05759b2426f069aR146.
`grep -nr 'await_sent' .`