Remove Dependent Keys On @tracked

[chadhietala]

As of #115 @tracked no longer requires the dependent keys. We need to do the following to unify this implementation with the one that Ember is going to expose. Below is a list of things we should do to align them:

• Add a deprecation for when a dependent key is passed.
• Ship version 0.11.0 with the deprecation
• Remove the DK deprecation and all the associated code
• Ship version 0.12.0 with the DK code gone