LU-6617 quota: remove quota migration code

LU-6617 quota: remove quota migration code

The quota migration code was used to migrate old quota admin
files into new format when upgrading system from old 2.1 system.

It can be removed now, anyone want to upgrade from such an old
system, and want to keep the quota limits settings at the same
time, one has to upgrade to an intermediate release to do the
migration first.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I41699157f07eba94453a86fe77a02189807ecbe8
Reviewed-on: http://review.whamcloud.com/14854
Tested-by: Jenkins
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>