Remove hydrator from collections

This line shouldn't exist. It shouldn't be necessary to add a hydrator to every collection you have in your project. In the ProductFieldset test asset, there is a collection and there isnt any hydrator for that collection, so we should follow the same pattern. 

This was a hack, introduced to get the tests pass, where they should fail, and this is responsible for hiding an error that should be fixed. Instead of adding a hydrator to that collection, the collection class setObject method should be fixed to proper handle nested collections.