autoreconf: drop support for old (< 1.8) aclocal versions

autoreconf: drop support for old (< 1.8) aclocal versions

The minimal automake and aclocal version required by the "most"
conservative important real world-projects (like Gnulib and Libvirt)
is 1.9 anyway (which is the version installed on old but still
supported installations of stable Distros like RHEL 5), so this
change should be safe and justified by now.

* bin/autoreconf.in (parse_args): Simplify by just assuming the aclocal
options '--force' and '--no-force' are supported and works correctly.
($aclocal_supports_force): Delete, no longer needed.
(run_aclocal): Heavily simplify by assuming that aclocal properly creates
'aclocal.m4' as lazily as possible.
* NEWS: Update.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>