Remove Ember.String.classify from ember-inflector

I think Ember.String.classify should be removed from ember-inflector
since it is provided by Ember.String itself.

I removed all tests as well. I even removed the test
_equal(Ember.String.classify('words'),'Word');_ which I think was
actually an error > it should
_equal(Ember.String.classify('words'),'Words');_.