rpc: remove some unused serialization code

The first commit of Nova contains this code as

 https://github.com/openstack/nova/blob/bf6e6e7/nova/rpc.py#L149

    try:
        publisher.send({'result': reply})
    except TypeError:
        publisher.send(
                {'result': dict((k, repr(v))
                                for k, v in reply.__dict__.iteritems())
                 })

but when the kombu driver was first added, it became:

 https://github.com/openstack/nova/blob/9cb46c48/nova/rpc/impl_kombu.py#L717

        try:
            msg = {'result': reply, 'failure': failure}
        except TypeError:
            msg = {'result': dict((k, repr(v))
                            for k, v in reply.__dict__.iteritems()),
                    'failure': failure}
        conn.direct_send(msg_id, msg)

Obviously, TypeError can't be raised with the current code and we dump
everything to json these days before passing down to kombu, qpid, etc.

Change-Id: I932fbfbbe824fbd9de8d31f070878e9db853ee45
Merge "rpc: remove some unused serialization code"