IB/qib: Remove qib multicast verbs functions

Multicast is now supported by rdmavt. Remove the verbs multicast functions
and use that.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Harish Chegondi <harish.chegondi@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>