Sub: remove unused TERRAIN_FOLLOW parameter

ArduSub/Parameters.cpp

@@ -586,15 +586,6 @@ const AP_Param::Info Sub::var_info[] = {
     // @Path: ../libraries/AP_Notify/AP_Notify.cpp
     GOBJECT(notify, "NTF_",  AP_Notify),
 
-#if AP_TERRAIN_AVAILABLE && AC_TERRAIN
-    // @Param: TERRAIN_FOLLOW
-    // @DisplayName: Terrain Following use control
-    // @Description: This enables terrain following for RTL and SURFACE flight modes. To use this option TERRAIN_ENABLE must be 1 and the GCS must  support sending terrain data to the aircraft.  In RTL the RTL_ALT will be considered a height above the terrain.  In LAND mode the vehicle will slow to LAND_SPEED 10m above terrain (instead of 10m above home).  This parameter does not affect AUTO and Guided which use a per-command flag to determine if the height is above-home, absolute or above-terrain.
-    // @Values: 0:Do Not Use in RTL and SURFACE,1:Use in RTL and SURFACE
-    // @User: Standard
-    GSCALAR(terrain_follow, "TERRAIN_FOLLOW", 0),
-#endif
-
     // @Group:
     // @Path: Parameters.cpp
     GOBJECT(g2, "",  ParametersG2),

ArduSub/Parameters.h

@@ -186,7 +186,7 @@ public:
         k_param_gcs_pid_mask = 178,
         k_param_throttle_filt,
         k_param_throttle_deadzone, // Used in auto-throttle modes
-        k_param_terrain_follow = 182,
+        k_param_terrain_follow = 182,   // deprecated
         k_param_rc_feel_rp,
         k_param_throttle_gain,
         k_param_cam_tilt_center, // deprecated
@@ -259,10 +259,6 @@ public:
     AP_Float        fs_ekf_thresh;
     AP_Int16        gcs_pid_mask;
 
-#if AP_TERRAIN_AVAILABLE && AC_TERRAIN
-    AP_Int8         terrain_follow;
-#endif
-
     AP_Int16        rc_speed; // speed of fast RC Channels in Hz
 
     AP_Float        gain_default;

ArduSub/Sub.h

@@ -572,7 +572,6 @@ private:
 #endif
     void terrain_update();
     void terrain_logging();
-    bool terrain_use();
     void init_ardupilot();
     void startup_INS_ground();
     bool position_ok();

ArduSub/terrain.cpp

@@ -27,12 +27,3 @@ void Sub::terrain_logging()
 #endif
 }
 
-// should we use terrain data for things including the home altitude
-bool Sub::terrain_use()
-{
-#if AP_TERRAIN_AVAILABLE && AC_TERRAIN
-    return (g.terrain_follow > 0);
-#else
-    return false;
-#endif
-}