IB/hfi1: Remove unused user command

The HFI1_CMD_SDMA_STATUS_UPD command was never implemented it has no
reason to live in the driver. Remove it.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mitko Haralanov <mitko.haralanov@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>