fs_mgr: Remove deprecated mount option

Mount option "nomblk_io_submit" was deleted from
upstream kernel v3.9 in 36ade451a5d736e61ac8302b64aacc5acb5e440f
and has not reappeared since then.
Now it only generates 'Ignoring removed nomblk_io_submit option'
in the logs

Test: manual
Change-Id: Ie609e7d3d38e808eeede1f1c55435ed027726025