Copter: precision landing does not use terrain database

precision landing was always only using the range finder, there was no use of the provided alt unless the rangefinder was good

ArduCopter/Copter.h

@@ -888,7 +888,6 @@ class Copter : public AP_Vehicle {
     // terrain.cpp
     void terrain_update();
     void terrain_logging();
-    bool terrain_use();
 
     // tuning.cpp
     void tuning();

ArduCopter/precision_landing.cpp

@@ -15,13 +15,9 @@ void Copter::update_precland()
 {
     int32_t height_above_ground_cm = current_loc.alt;
 
-    // use range finder altitude if it is valid, else try to get terrain alt
+    // use range finder altitude if it is valid, otherwise use home alt
     if (rangefinder_alt_ok()) {
         height_above_ground_cm = rangefinder_state.alt_cm;
-    } else if (terrain_use() && !current_loc.is_zero()) {
-        if (!current_loc.get_alt_cm(Location::AltFrame::ABOVE_TERRAIN, height_above_ground_cm)) {
-            height_above_ground_cm = current_loc.alt;
-        }
     }
 
     precland.update(height_above_ground_cm, rangefinder_alt_ok());

ArduCopter/terrain.cpp

@@ -26,13 +26,3 @@ void Copter::terrain_logging()
     }
 #endif
 }
-
-// should we use terrain data for things including the home altitude
-bool Copter::terrain_use()
-{
-#if AP_TERRAIN_AVAILABLE && AC_TERRAIN
-    return (g.terrain_follow > 0);
-#else
-    return false;
-#endif
-}