Update the BIO_s_connect documentation after the BIO refactoring.

The BIO was refactored in 417be660

,
but the manual wasn't fully updated to reflect some of the changes.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/5007)