AP_Follow: use ahrs singleton

libraries/AP_Follow/AP_Follow.cpp

@@ -114,8 +114,7 @@ const AP_Param::GroupInfo AP_Follow::var_info[] = {
    constructor is not called until detect() returns true, so we
    already know that we should setup the proximity sensor
 */
-AP_Follow::AP_Follow(const AP_AHRS &ahrs) :
-        _ahrs(ahrs),
+AP_Follow::AP_Follow() :
         _p_pos(AP_FOLLOW_POS_P_DEFAULT)
 {
     AP_Param::setup_object_defaults(this, var_info);
@@ -158,7 +157,7 @@ bool AP_Follow::get_target_dist_and_vel_ned(Vector3f &dist_ned, Vector3f &dist_w
 {
     // get our location
     Location current_loc;
-    if (!_ahrs.get_position(current_loc)) {
+    if (!AP::ahrs().get_position(current_loc)) {
          return false;
      }
 

libraries/AP_Follow/AP_Follow.h

@@ -36,7 +36,7 @@ public:
     };
 
     // constructor
-    AP_Follow(const AP_AHRS &ahrs);
+    AP_Follow();
 
     // set which target to follow
     void set_target_sysid(uint8_t sysid) { _sysid = sysid; }
@@ -87,9 +87,6 @@ private:
     // get offsets in meters in NED frame
     bool get_offsets_ned(Vector3f &offsets) const;
 
-    // references
-    const AP_AHRS &_ahrs;
-
     // parameters
     AP_Int8     _enabled;           // 1 if this subsystem is enabled
     AP_Int16    _sysid;             // target's mavlink system id (0 to use first sysid seen)