RDMA/rxe: Remove redundant num_sge fields

RDMA/rxe: Remove redundant num_sge fields

In include/uapi/rdma/rdma_user_rxe.h there are redundant copies of num_sge
in the rxe_send_wr, rxe_recv_wqe, and rxe_dma_info. Only the ones in
rxe_dma_info are actually used by the rxe kernel driver.

The userspace would set these values, but the kernel never read them.

This change has no affect on the current ABI and new or old versions of
rdma-core operate correctly with new or old versions of the kernel rxe
driver.

Link: https://lore.kernel.org/r/20220913222716.18335-1-rpearsonhpe@gmail.com
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>