igc: Remove unused IGC_ICS_DRSTA define

Device reset assert for interrupt cause register not in
use for i225 device.
This patch comes to clean up this define.
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

@@ -244,7 +244,6 @@
 /* Interrupt Cause Set */
 #define IGC_ICS_LSC		IGC_ICR_LSC       /* Link Status Change */
 #define IGC_ICS_RXDMT0		IGC_ICR_RXDMT0    /* rx desc min. threshold */
-#define IGC_ICS_DRSTA		IGC_ICR_DRSTA     /* Device Reset Aserted */
 
 #define IGC_ICR_DOUTSYNC	0x10000000 /* NIC DMA out of sync */
 #define IGC_EITR_CNT_IGNR	0x80000000 /* Don't reset counters on write */