Revert "lan78xx: add ndo_get_stats64"

This reverts commit a59f8c5b.

There are several bugs in this new code, for example:

1) Uses sleeping locks in get_stats64, which is not allowed,
   as the operation can be invoked in an atomic context.

2) Uses PM fields without CONFIG_PM or similar guards.

3) Does not synchronize HW stats when the device runtime
   suspends.

Therefore this is being reverted until a correct version
is implemented.

Signed-off-by: David S. Miller <davem@davemloft.net>