TLS: Use EVP_PKEY_get_group_name() to get the group name

TLS: Use EVP_PKEY_get_group_name() to get the group name

For the moment, we translate the result to a NID, because that's still
used in several locations in libssl.  Future development should change
all the internals to be name based instead.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/13436)