igc: Remove unneeded ICTXQMTC register

Tx Queue Min Threshold Count register no applicable for the i225 device.
This patch comes to clean up it.

Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>