openssl: don't build tests

These require shared libraries and we save a tiny amount of build time.
Fixes:
http://autobuild.buildroot.net/results/88e/88e5e07e94e49879907186ff35ce66944f867ec2/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>