The pseudo-internal MarshalState and UnmarshalState method should
not have a seperate Message argument since it is passed in through
the extensible MarshalInput and UnmarshalInput values.
Change-Id: I838aadaee30e91cdf888ab024e65348c73c1cd7e
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/222678
Reviewed-by: Damien Neil <dneil@google.com>