Reduce all uses of Unstructured to the simpler form, and avoid asking
for mapper or typer unless it is required. Use Typed() for places that
previously used VersionedObject, and remove paths for versioned objects
from code that is now using unstructured.
Previously, the fake RESTClient in client-go required a Registry. It
used the Registry to fetch the GroupVersion for the fake client.
However, the way it did so was dubious in some cases (it hard-coded the
default API group in places), and not strictly necssary.
This updates the fake client to just recieve the GroupVersion and
internal group name directly, instead of requiring a Registry, so that
it can be consumed in unit tests where a Registry isn't necessarily
readily available (e.g. elsewhere in client-go).
