MFC r280757: Remove request sorting from GEOM_MIRROR and GEOM_RAID.

When CPU is not busy, those queues are typically empty. When CPU is busy,
then one more extra sorting is the last thing it needs. If specific device
(HDD) really needs sorting, then it will be done later by CAM.

This supposed to fix livelock reported for mirror of two SSDs, when UFS
fires zillion of BIO_DELETE requests, that totally blocks I/O subsystem by
pointless sorting of requests and responses under single mutex lock.