Remove --tls-export-cert

Remove --tls-export-cert

As OpenVPN 2.6+ is doing some adoptions to the license text, all
prior contributors need to accept this new text.  Unfortunately, Mathieu
Giannecchini who implemented the --tls-export-cert feature did not
respond at all.  Without an explicit acceptance we need to remove this
feature to avoid potential legal complications.

If this is still a wanted feature, it will need to be re-implemented
from scratch.

Signed-off-by: David Sommerseth <davids@openvpn.net>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20231122143101.58483-1-dazo+openvpn@eurephia.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg27557.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>