Remove/refactor all leftover piston code

[dshafer]

There are several instances of old piston code in DDA which, if hit, produce very difficult-to-debug errors. Example: https://github.com/salesforce/django-declarative-apis/blob/master/django_declarative_apis/resources/resource.py#L222

This line returns an incompatible type for the method. If hit, this line causes an internal error in Django that entirely swallows the original stack trace.

We need to excise all of this leftover code, and increase test coverage to catch all corner/error cases in machinery/resources