igc: Fix double definitions

Collision threshold and threshold's shift has been defined twice.
This patch comes to fix that.
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>

drivers/net/ethernet/intel/igc/igc_defines.h

@@ -264,9 +264,6 @@
 #define IGC_TCTL_RTLC		0x01000000 /* Re-transmit on late collision */
 #define IGC_TCTL_MULR		0x10000000 /* Multiple request support */
 
-#define IGC_CT_SHIFT			4
-#define IGC_COLLISION_THRESHOLD		15
-
 /* Flow Control Constants */
 #define FLOW_CONTROL_ADDRESS_LOW	0x00C28001
 #define FLOW_CONTROL_ADDRESS_HIGH	0x00000100