Fix failing build with Ember beta and canary

[bmac]

It looks like something changed with the recent Ember beta that caused values that are provided to Ember.Object.create() to get stored on meta and cleared out when the object is destroyed.

Ember Data was injecting _internalModel into the model when its created here. On Ember 2.8.0 the _internalModel property was still available after the model was destroyed. In the Ember 2.9.0-beta.3 record._internalModel is no longer accessible after a record has been destroyed.

cc @rwjblue @stefanpenner

[rwjblue]

#4545 also fixes