autoconf: Fix engine checks for openssl 1.1

autoconf: Fix engine checks for openssl 1.1

In openssl 1.1, ENGINE_cleanup became a #define instead of a function
(because it's no longer needed as engines are self cleaning).  Update
the autoconf.ac script to check for ENGINE_cleanup as a declaration to
avoid falsely undefinig HAVE_OPENSSL_ENGINE in openssl 1.1+

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <1509291288.3116.14.camel@HansenPartnership.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15676.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>