Remove the never-functional no-sct

It was added as part of 2df84dd3


but has never actually been used for anything; presumably it was
a typo for one of SCTP or CT.

This removes the last '??' entry from INSTALL.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>