AntennaTracker: always build with MAVLink2 headers

AntennaTracker/GCS_Mavlink.cpp

@@ -888,11 +888,9 @@ mission_failed:
         send_autopilot_version(FIRMWARE_VERSION);
         break;
 
-#if MAVLINK_PROTOCOL_VERSION >= 2
     case MAVLINK_MSG_ID_SETUP_SIGNING:
         handle_setup_signing(msg);
         break;
-#endif
     } // end switch
 } // end handle mavlink