Do not load certificate from tls_ctx_use_external_private_key()

Do not load certificate from tls_ctx_use_external_private_key()

The cert and key loading logic surrounding management-external-key and
management-external cert was somewhat intertwined.  Untangle these to
prepare for making the external key code more reusable.

The best part is that this even reduces the number of lines of code.

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1536916459-25900-1-git-send-email-steffan.karger@fox-it.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17464.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>