EVP_PKEY_CTX_set_dh_ functions were only available when DH was enabled
('no-dsa' not configured).  However, that makes it impossible to use
these functions with an engine or a provider that happens to implement
DH.  This change solves that problem by shuffling these functions to
more appropriate places.

By consequence, there are a number of places where we can remove the
check of OPENSSL_NO_DH.  This requires some re-arrangements of
internal tables to translate between numeric identities and names.

Partially fixes #13550

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/13589)