autogen.sh: Don't set AUTO{CONF|MAKE}_VERSION and WANT_AUTO{CONF|MAKE}

autogen.sh: Don't set AUTO{CONF|MAKE}_VERSION and WANT_AUTO{CONF|MAKE}

On some systems (for example Gentoo Linux, FreeBSD, and OpenBSD), these
variables are used to select which version of GNU automake and autoconf
to use, but we shouldn't depend on a specific version -- instead we
should use the "system default". So probably it is up to the user to
set these variables accordingly to set up some wrapper scripts of his
operating system distribution.