igb: Remove invalid stats counters

There are several counters being used like they are static when in fact
they are clear on read.  In order to prevent the values from being
incorrect I am removing the defunct counters.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>