Prevent new resource instances from readying the parentObject.

When we destroyed a new object, we checked if the parentObject was
ready. This wasn't really necessary, since we didn't have a URL we
needed to destroy or anything. Our destruction was internal only.

By removing the parentObject.ready call in this case, we get faster
destruction for unsaved/unloaded objects, and we also prevent a problem
where we may not be in a position to even fetch the parent object.

The case I refer to is the destruction of draft comments on draft
reviews, when not logged in. I have a fix I'll put out after this, which
prevents trying to get the draft review if not logged in. In this case,
we'd error out, which would break the ready() call. We don't even want
to hit that case for new objects, though. New objects should be
destroyable without the parent object being fetchable.

As part of this, I've standardized the call to the parent destroy
function and the success callback to it, so that we make sure to reset
the state in all cases.

Tested with my other change, which allowed us to successfully delete
draft comments when not logged in.