Move ember-states into a plugin: https://github.com/emberjs/ember-states

There are no more dependencies on ember-states in Ember.js itself, or in Ember Data. If you depend on it, please use a build from the plugin's repo.
Throw error if Ember.StateManager or Ember.State classes are used without the ember-states plugin installed
Merge pull request #3191 from emberjs/remove-ember-states

Move ember-states into a plugin