LU-6972 llite: get rid of unused ll_super_blocks list

LU-6972 llite: get rid of unused ll_super_blocks list

ll_super_blocks became unused quite a while ago with switch
to the new CLIO code.
So this patch removes the list, ll_sb_lock spinlock that guards it
and superblock info ll_list linkage.

Change-Id: If0af4f4c05f45feaedc54ca57f0d1106ad7cabe3
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-on: http://review.whamcloud.com/15922
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>