Remove LibreSSL specific defines not needed for modern LibreSSL

Remove LibreSSL specific defines not needed for modern LibreSSL

Most of the functions remove were either already have a version check
against LibreSSL 2.9.0 or are also now deprecated in LibreSSL as well
according to the man pages in OpenBSD 6.8 like SSL_CTX_set_ecdh_auto
and SSL_library_init.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Antonio Quartulli <antonio@openvpn.net>
Message-Id: <20210415114541.1001644-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22119.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>