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

This allows removing duplicated code

libraries/SITL/SIM_ADSB.cpp

@@ -190,10 +190,10 @@ void ADSB::send_report(void)
             ADSB_Vehicle &vehicle = vehicles[i];
             Location loc = home;
 
-            location_offset(loc, vehicle.position.x, vehicle.position.y);
+            loc.offset(vehicle.position.x, vehicle.position.y);
 
             // re-init when exceeding radius range
-            if (get_distance(home, loc) > _sitl->adsb_radius_m) {
+            if (home.get_distance(loc) > _sitl->adsb_radius_m) {
                 vehicle.initialised = false;
             }
             

libraries/SITL/SIM_Aircraft.cpp

@@ -180,7 +180,7 @@ bool Aircraft::on_ground() const
 void Aircraft::update_position(void)
 {
     location = home;
-    location_offset(location, position.x, position.y);
+    location.offset(position.x, position.y);
 
     location.alt  = static_cast<int32_t>(home.alt - position.z * 100.0f);
 
@@ -683,7 +683,7 @@ void Aircraft::smooth_sensors(void)
     smoothing.position += smoothing.velocity_ef * delta_time;
 
     smoothing.location = home;
-    location_offset(smoothing.location, smoothing.position.x, smoothing.position.y);
+    smoothing.location.offset(smoothing.position.x, smoothing.position.y);
     smoothing.location.alt  = static_cast<int32_t>(home.alt - smoothing.position.z * 100.0f);
 
     smoothing.last_update_us = now;

libraries/SITL/SIM_XPlane.cpp

@@ -306,9 +306,9 @@ bool XPlane::receive_data(void)
     accel_earth.z += GRAVITY_MSS;
     
     // the position may slowly deviate due to float accuracy and longitude scaling
-    if (get_distance(loc, location) > 4 || abs(loc.alt - location.alt)*0.01f > 2.0f) {
+    if (loc.get_distance(location) > 4 || abs(loc.alt - location.alt)*0.01f > 2.0f) {
         printf("X-Plane home reset dist=%f alt=%.1f/%.1f\n",
-               get_distance(loc, location), loc.alt*0.01f, location.alt*0.01f);
+               loc.get_distance(location), loc.alt*0.01f, location.alt*0.01f);
         // reset home location
         position_zero(-pos.x, -pos.y, -pos.z);
         home.lat = loc.lat;