FIX: removes legacy Ember.keys usage causing a crash (PR #13085)

The crash:

Uncaught TypeError: Ember.keys is not a function

Repro:

  • visit home page
  • click new topic
  • navigate to your messages by clicking your avatar (top right), then enveloppe icon, and finally the bottom chevron
  • click New Message
  • click cancel in the composer, it should crash

GitHub