devlink: drop leftover duplicate/unused code

The recent merge from net left-over some unused code in
leftover.c - nomen omen.

Just drop the unused bits.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>