Remove unused variables from ssl_verify_openssl.c extract_x509_extension()

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1414230851-5350-1-git-send-email-steffan@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9195
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 6e469f46e94b2bd0fc1509f2bfbda4d6b5374b14)