[SCSI] scsi_dh: Remove hardware handler infrastructure from dm

This patch just removes infrastructure that provided support for hardware
handlers in the dm layer as it is not needed anymore.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Acked-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>