clean up the tar-gz patch a bit

remove the temp hardlink
don't really need format arg
hook tar-gz format in a bit

cli/koji

@@ -5354,7 +5354,7 @@ def handle_image_build(options, session, args):
     formats = ('vmdk', 'qcow', 'qcow2', 'vdi', 'vpc', 'rhevm-ova',
                'vsphere-ova', 'vagrant-virtualbox', 'vagrant-libvirt',
                'vagrant-vmware-fusion', 'docker', 'raw-xz',
-               'liveimg-squashfs')
+               'liveimg-squashfs', 'tar-gz')
     usage = _("usage: %prog image-build [options] <name> <version> " +
               "<target> <install-tree-url> <arch> [<arch>...]")
     usage += _("\n       %prog image-build --config FILE")