LU-6822 nrs: remove obsolete assertion in nrs_orr_start()

LU-6822 nrs: remove obsolete assertion in nrs_orr_start()

kmem_cache_destroy() doesn't return any value, so we should remove
this obsolete assertion, otherwise LBUG will happen when orr policy
is enabled.

Signed-off-by: Emoly Liu <emoly.liu@intel.com>
Change-Id: I240e7bd660a6960b1e29da3575388a966ce8dca9
Reviewed-on: http://review.whamcloud.com/15540
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>