Remove dead remains of extract_x509_field_test

Remove dead remains of extract_x509_field_test

This removes some leftover references to extract_x509_field_test that
was removed 15 years ago in commit 564cbab5f.

Change-Id: Ie511a586cf022afcab9d67891ff80676ac7d47b9
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20231201111846.15097-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg27625.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>