migration/rdma: Drop RDMARegister.key.chunk Not used anymore. Reviewed-by: Jinpu Wang <jinpu.wang@cloud.ionos.com> Signed-off-by: Peter Xu <peterx@redhat.com> Reviewed-by: Jack Wang <jinpu.wang@cloud.ionos.com> Signed-off-by: Fabiano Rosas <farosas@suse.de>