Remove --disable-def-auth configure argument

Remove --disable-def-auth configure argument

With scripts, plugin and management interface now all supporting
deferred auth, maintaining support of --disbale-def-auth becomes more
of a burden and the few kilobyte in potential binary size do not
outweigh this. Also the code in ssl_verify is hard to hard because
all the ifdefs.

Especially for management interface there are so many features not
directly related to deferred that depend on MANAGEMENT_DEF_AUTH
(like client-kill) that supporting management without deferred auth
is not worth it anymore. And removing this remover a high number of
ifdefs in manage.c/h

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20201023113244.26295-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg21214.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>