LU-9995 lfsck: keep the LMV_HASH_FLAG_DEAD flag

LU-9995 lfsck: keep the LMV_HASH_FLAG_DEAD flag

Since lustre 2.8, the flag LMV_HASH_FLAG_DEAD is not needed, instead
this DEAD and orphan flags will be stored in LMA (see LMAI_ORPHAN).
At that time, we kept such flag for LFSCK to handle the filesystem
upgrading from old release (Lustre-2.7 or older). Lustre-2.11 may
still needs to support the upgrading from Lustre-2.7 (mainly consider
the EE users), we will continuously keep such flag for a while.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I11c1fa5a354d5f244514c10e3ca2c9e952eef975
Reviewed-on: https://review.whamcloud.com/29130
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>