igc: Remove dead code related to flower filter

IGC driver has no support for tc-flower filters so this patch removes
some leftover code, probably copied from IGB driver by mistake.

Signed-off-by: Andre Guedes <andre.guedes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>