crypto: improve errors in DiffieHellmanGroup

1. The DiffieHellmanGroup class is only instantiated from within
   Node.js, which always passes exactly one argument.
2. Use the existing ERR_CRYPTO_UNKNOWN_DH_GROUP error code for the
   existing "Unknown group" error. The message has not been changed
   to prevent breaking existing applications.

PR-URL: https://github.com/nodejs/node/pull/31445


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>