staging/rdma/hfi1: Removing unused struct hfi1_verbs_counters

It removes the unused struct hfi1_verbs_counters from verbs.h

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Sebastian Sanchez <sebastian.sanchez@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>