e1000e: remove definition of struct which is no longer used

The e1000e driver has been converted to use extended descriptors instead of
the older legacy descriptor type.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>