AC_Circle: remove _rangefinder_use parameter

We will reuse the WPNAV_RFND_USE parameter indirectly

libraries/AC_WPNav/AC_Circle.cpp

@@ -312,7 +312,7 @@ void AC_Circle::init_start_angle(bool use_heading)
 AC_Circle::TerrainSource AC_Circle::get_terrain_source() const
 {
     // use range finder if connected
-    if (_rangefinder_available && _rangefinder_use) {
+    if (_rangefinder_available) {
         return AC_Circle::TerrainSource::TERRAIN_FROM_RANGEFINDER;
     }
 #if AP_TERRAIN_AVAILABLE

libraries/AC_WPNav/AC_Circle.h

@@ -140,7 +140,6 @@ private:
     // terrain following variables
     bool        _terrain_alt;           // true if _center.z is alt-above-terrain, false if alt-above-ekf-origin
     bool        _rangefinder_available; // true if range finder could be used
-    AP_Int8     _rangefinder_use;       // true if caller has requested rangefinder be used for terrain altitude
     bool        _rangefinder_healthy;   // true if range finder is healthy
     float       _rangefinder_alt_cm;    // latest rangefinder altitude
 };