igb: Remove obsolete workaround for Windows

I confirmed it works with Windows even without this workaround. It is
likely to be a mistake so remove it.

Fixes: 3a977dee ("Intrdocue igb device emulation")
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>