Fix function names in ct(7) documentation

The correct function name is SSL_CTX_enable_ct, not SSL_CTX_ct_enable.

Signed-off-by: Christian Heimes <christian@python.org>

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7916)