LU-2235 lfsck: remove unnecessary warning message

LU-2235 lfsck: remove unnecessary warning message

Currently, the new online LFSCK does not work for ZFS backend,
but it is neither fatal nor block the mount processing.
So remove those unnecessary warning message.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Change-Id: I106a6b5c978cde8695821776570c30605f03c400
Reviewed-on: http://review.whamcloud.com/4452
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Prakash Surya <surya1@llnl.gov>