Cleaned up compositeView.onBeforeRender spec

I actually don't want to make this change because there are some cases where it wouldn't work, and would be an inconsistency across tests.

```js
this.fooHandlerStub = this.sinon.stub();

this.View = Marionette.View.extend({
  modelEvents: {'foo': 'fooHandler'},
  fooHandler: this.fooHandlerStub
});
```

Could not be written as:

```js
this.View = Marionette.View.extend({
  modelEvents: {'foo': 'fooHandler'}
});

this.fooOneStub = this.sinon.stub(this.view, 'fooOne');
```

because sinon would throw an error:
```js
TypeError: Cannot stub non-existent own property fooOne
```

So you could make the rule that you only stub existing methods this way which would lead to:

```js
this.fooHandlerStub = this.sinon.stub();

this.View = Marionette.View.extend({
  modelEvents: {'foo': 'fooHandler'},
  fooHandler: this.fooHandlerStub
});

this.renderStub = this.sinon.stub(this.View.prototype, 'render');
```

but that puts your stubs and spies in two different places.

so :-1: