btrfs: remove stale test for alien devices from auto group

btrfs: remove stale test for alien devices from auto group

btrfs/198 is supposed to be a test for the patch
"btrfs: remove identified alien device in open_fs_devices" but this patch
was never merged in btrfs.

Remove the test from fstests' auto group, as it is constantly failing.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>