Remove the ability to create a custom EVP_PKEY_ASN1_METHOD

Remove the ability to create a custom EVP_PKEY_ASN1_METHOD

Now that the ability to register a custom EVP_PKEY_ASN1_METHOD has
been removed in an earlier commit, we can now remove the functions that
are used to create a custom EVP_PKEY_ASN1_METHOD.

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/29405)