RDMA/netlink: Remove unused data structure

Delete structure which is not connected due to removal in commit
cited in Fixes line.

Fixes: a78e8723

 ("RDMA/cma: Remove CM_ID statistics provided by rdma-cm module")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>