RDMA/core: Remove unused req_ncomp_notif device operation

The request_ncomp_notif device operation and function are unused, remove
them.

Link: https://lore.kernel.org/r/20210311150921.23726-1-galpress@amazon.com


Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>