do_sigver_init: Remove fallback for missing provider implementations.
do_sigver_init: Remove fallback for missing provider implementations.

We now have everything implemented in providers.

Reviewed-by: Paul Dale <ddec78389666b4f7c9b4d110380c848489a3e4aa@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14404)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl