Plane: make the defaut for FS_GCS_ENABL clearer

ArduPlane/Parameters.pde

@@ -443,7 +443,7 @@ const AP_Param::Info var_info[] PROGMEM = {
     // @Description: Enable ground control station telemetry failsafe. Failsafe will trigger after FS_LONG_TIMEOUT seconds of no MAVLink heartbeat messages. There are two possible enabled settings. Seeing FS_GCS_ENABL to 1 means that GCS failsafe will be triggered when the aircraft has not received a MAVLink HEARTBEAT message. Setting FS_GCS_ENABL to 2 means that GCS failsafe will be triggerded on either a loss of HEARTBEAT messages, or a RADIO_STATUS message from a MAVLink enabled 3DR radio indicating that the ground station is not receiving status updates from the aircraft, which is indicated by the RADIO_STATUS.remrssi field being zero (this may happen if you have a one way link due to asymmetric noise on the ground station and aircraft radios). WARNING: Enabling this option opens up the possibility of your plane going into failsafe mode and running the motor on the ground it it loses contact with your ground station. If this option is enabled on an electric plane then you should enable ARMING_REQUIRED. 
     // @Values: 0:Disabled,1:Heartbeat,2:HeartbeatAndREMRSSI
     // @User: Standard
-    GSCALAR(gcs_heartbeat_fs_enabled, "FS_GCS_ENABL", GCS_HEARTBEAT_FAILSAFE),
+    GSCALAR(gcs_heartbeat_fs_enabled, "FS_GCS_ENABL", GCS_FAILSAFE_OFF),
 
     // @Param: FLTMODE_CH
     // @DisplayName: Flightmode channel

ArduPlane/config.h

@@ -260,8 +260,6 @@
 // THROTTLE_FS_VALUE
 // SHORT_FAILSAFE_ACTION
 // LONG_FAILSAFE_ACTION
-// GCS_HEARTBEAT_FAILSAFE
-//
 #ifndef THROTTLE_FAILSAFE
  # define THROTTLE_FAILSAFE              ENABLED
 #endif
@@ -274,10 +272,6 @@
 #ifndef LONG_FAILSAFE_ACTION
  # define LONG_FAILSAFE_ACTION           0
 #endif
-#ifndef GCS_HEARTBEAT_FAILSAFE
- # define GCS_HEARTBEAT_FAILSAFE         DISABLED
-#endif
-
 
 //////////////////////////////////////////////////////////////////////////////
 // AUTO_TRIM