igc: Remove obsolete mask

'IGC_CTRL_EXT_LINK_MODE_MASK' not in use. This patch comes to tidy up
obsolete define.

Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Nechama Kraus <nechamax.kraus@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

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

@@ -85,9 +85,6 @@
 
 #define IGC_WUFC_EXT_FILTER_MASK GENMASK(31, 8)
 
-/* Physical Func Reset Done Indication */
-#define IGC_CTRL_EXT_LINK_MODE_MASK	0x00C00000
-
 /* Loop limit on how long we wait for auto-negotiation to complete */
 #define COPPER_LINK_UP_LIMIT		10
 #define PHY_AUTO_NEG_LIMIT		45