CORE & PROV: clean away OSSL_FUNC_mac_size()

CORE & PROV: clean away OSSL_FUNC_mac_size()

There was a remaining function signature declaration, but no
OSSL_DISPATCH number for it nor any way it's ever used.  It did exist
once, but was replaced with an OSSL_PARAM item to retrieve.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14048)