ibmveth: remove procfs code

We export all the driver specific statistics via ethtool, so there is no need
to duplicate this in procfs.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Santiago Leon <santil@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>