Remove test handled by backbone.babysitter

In this test's current form, it is really only duplicating test's in marionette and in babysitter.

This test instantiates a `CollectionView`
``` 
this.collectionView = new Marionette.CollectionView();
```
which calls `_initChildViewStorage` in the constructor creating the babysitter children container
http://marionettejs.com/annotated-src/backbone.marionette#section-307

It goes on to add a view to that container:
```
this.collectionView.children.add(new Backbone.View());
```
and then 
```
expect(this.collectionView.children.length).to.equal(1);
```

The children is indirectly tested in this fashion throughout the collection-view tests however, very similarly tested here:

https://github.com/marionettejs/backbone.marionette/blob/minor/test/unit/collection-view.spec.js#L305

And then fairly explicitly tested almost exactly in babysitter here:
https://github.com/marionettejs/backbone.babysitter/blob/master/spec/javascripts/childviewContainer.spec.js#L44