Copter: replace location_offset() and get_distance() function calls with Location object member function calls

This allows removing duplicated code

ArduCopter/commands.cpp

@@ -107,7 +107,7 @@ bool Copter::far_from_EKF_origin(const Location& loc)
 {
     // check distance to EKF origin
     const struct Location &ekf_origin = inertial_nav.get_origin();
-    if (get_distance(ekf_origin, loc) > EKF_ORIGIN_MAX_DIST_M) {
+    if (ekf_origin.get_distance(loc) > EKF_ORIGIN_MAX_DIST_M) {
         return true;
     }
 

ArduCopter/navigation.cpp

@@ -14,7 +14,7 @@ void Copter::run_nav_updates(void)
 uint32_t Copter::home_distance()
 {
     if (position_ok()) {
-        _home_distance = get_distance_cm(current_loc, ahrs.get_home());
+        _home_distance = current_loc.get_distance(ahrs.get_home()) * 100;
     }
     return _home_distance;
 }