Registration - 2 Remove access_token from client metadata

The access_token listed in Client Metadata seems to be vestigial from when this was a list of query parameters. As it stands right now, it's unclear whether the client is supposed to include this parameter in the JSON object used in the registration (and eventual update) requests.

I would suggest removing this entirely from this section, as its functionality is already covered in the intro paragraphs of § 3.