Drop support for {{translateAttr}}

Dropping for a variety of reasons:

 * It doesn't  support bound values, which confuses users
 * Users can achieve the same effect with `TranslateableAttributes` or by creating translated properties on the controller or component
 * It doesn't play nicely with the current HTMLbars-Handlebars compatibility layer

See https://github.com/emberjs/ember.js/issues/9961