autoreconf: assume --force-missing automake option is supported

autoreconf: assume --force-missing automake option is supported

According to Automake's NEWS file, it is since at least Automake 1.8,
and in autoreconf we are already assuming aclocal >= 1.8 anyway.

* bin/autoreconf.in (parse_args): Simplify a little by just assuming
the automake option '--force-missing' is supported.
($automake_supports_force_missing): Delete, no longer needed.
* NEWS: Update.

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