Remove check for socket functions and Win XP compatbility code

Remove check for socket functions and Win XP compatbility code

While the check if all socket related functions are present sounds like
a good idea in theory, in reality it just adds time to configure runs.

Our poll check on windows is currently only depending on sys/poll.h
non-existance. Make the check and comment more explicit.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20210406162518.4075-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22052.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>