igc: Remove obsolete define

'MII_CR_FULL_DUPLEX' define not in use. This patch comes to tidy up
 obsolete define.
Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

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

@@ -581,7 +581,6 @@
 #define IGC_GEN_POLL_TIMEOUT	1920
 
 /* PHY Control Register */
-#define MII_CR_FULL_DUPLEX	0x0100  /* FDX =1, half duplex =0 */
 #define MII_CR_RESTART_AUTO_NEG	0x0200  /* Restart auto negotiation */
 #define MII_CR_POWER_DOWN	0x0800  /* Power down */
 #define MII_CR_AUTO_NEG_EN	0x1000  /* Auto Neg Enable */