Fix hiding of review reply draft banners.
Review Request #8505 — Created Oct. 27, 2016 and submitted
Trivial fix for hiding the reply draft banners when the draft state changes.
Created a draft reply, then hit "discard". Saw the reply banner disappear.
Tool: Pyflakes Ignored Files: reviewboard/static/rb/js/views/reviewView.es6.js Tool: PEP8 Style Checker Ignored Files: reviewboard/static/rb/js/views/reviewView.es6.js