Deprecate the low level HMAC functions

Deprecate the low level HMAC functions

Use of the low level HMAC functions has been informally discouraged for a
long time.  We now formally deprecate them.

Applications should instead use EVP_MAC_CTX_new(3), EVP_MAC_CTX_free(3),
EVP_MAC_init(3), EVP_MAC_update(3) and EVP_MAC_final(3).

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10836)