Remove ARCH packaging

Remove ARCH packaging

The kernel modules are now available in the Arch User Repository
(AUR) via zfs.  Since their packaging is maintained and superior
to ours it is being removed from the tree.

  https://wiki.archlinux.org/index.php/ZFS

Now that various distributions are picking up the packages we
should eventually be able to remove most of this infrastructure.
Packaging belongs with the distributions not upstream.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>