Remove the KSorts file that still used the old String representation for Sort

Picking up from where @yilongli left it.
@dwightguth please review.
Isn't this what we are trying to avoid? If we need something to be a sort, then make sure that we are putting a sort in there. In any case, since `node.getAttribute` returns a string, should go through the validation of `Sort.of`. If we don't have any restrictions for the name of the sort, then we may add some in the future. I could revert this file if you feel otherwise.