igc: Remove unused code

Remove unused igc_adv_data_desc definition from igc_base.h file.
Descriptors definition will be added per demand.

Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>