btrfs/219: add to the auto group

Add this test case back to the auto group which reverts the
commit e2e7b549380a ("fstests: btrfs/219: remove it from auto group") since
the previously missing kernel commit 5f58d783fd78 ("btrfs: free device in
btrfs_close_devices for a single device filesystem") has already been
integrated.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>