Fix building with LibreSSL 2.5.1 by cleaning a hack.

Fix building with LibreSSL 2.5.1 by cleaning a hack.

Similar to what is done in curl: https://github.com/curl/curl/blob/028391df5d84d9fae3433afdee9261d565900355/lib/vtls/openssl.c#L603-L619

Use SSL_CTX_get0_privatekey() for OpenSSL >= 1.0.2

Signed-off-by: Olivier Wahrenberger <olivierw.ml@gmail.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20170213183826.73008-1-O2Graphics@users.noreply.github.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14045.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>