Remove obsolete error constant CT_F_CTLOG_NEW_NULL

ctlog_new_null() no longer exists.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1554)
(cherry picked from commit 333c2e43)