contrib: Remove keychain-mcd code

contrib: Remove keychain-mcd code

After the security audits performed by Cryptography Engineering the
spring of 2017 [1], there were several concerns about the contrib code
for the macOS keychain support.  After more careful review of this
code base, it was considered to be in such a bad shape that it will
need a massive overhaul.  There were more issues than what the security
audit revealed.

It was attempted several times to get in touch with the contributor
of this code; with no response at all [2].  There has however
been some discussions with the Tunnelblick project [3]. There is one
person there willing to go through this and improve the situation.
The main Tunnelblick maintainer is also willing to include the improved
code to their project instead of having this as a contrib code in
the upstream OpenVPN project.

So this patch just removes the code which we will no longer
ship as part of OpenVPN - and the Tunnelblick project will take
over the responsibility for this code base on their own.  And since
this code base is purely macOS specific, this seems to be a far
better place for this code to reside.

Signed-off-by: David Sommerseth <davids@openvpn.net>
[1]
<http://community.openvpn.net/openvpn/wiki/QuarkslabAndCryptographyEngineer
Audits#OVPN-04-1:PossibleNULLpointerderefenceincontribkeychain-mcdcert_data
.c>
[2]
<https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14559.
html>
[3] <https://github.com/Tunnelblick/Tunnelblick/pull/369>
Acked-by: Jonathan K. Bullard <jkbullard@gmail.com>
Message-Id: <20170725130314.12919-1-davids@openvpn.net>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15130.html
Signed-off-by: David Sommerseth <davids@openvpn.net>