This reverts commit ea84a82f77.
This is causing problems with `/theme-qunit` on legacy, non-ember-cli production sites. Reverting while we work on a fix
This is quite complex as it means that in production we have to build
Ember CLI test files and allow them to be used by our Rails application.
There is a fair bit of glue we can remove in the future once we move to
Ember CLI completely.