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

This allows removing duplicated code

libraries/AP_Scripting/lua_bindings.cpp

@@ -219,8 +219,7 @@ static int location_distance(lua_State *L) {
         return luaL_argerror(L, args, "too many arguments");
     }
 
-    lua_pushnumber(L, get_distance(*check_location(L, -2),
-                                   *check_location(L, -1)));
+    lua_pushnumber(L, *check_location(L, -2).get_distance(*check_location(L, -1)));
 
     return 1;
 }
@@ -272,7 +271,7 @@ static int location_offset(lua_State *L) {
         return luaL_argerror(L, args, "too many arguments");
     }
 
-    location_offset(*check_location(L, -3),
+    *check_location(L, -3).offset(
                     luaL_checknumber(L, -2),
                     luaL_checknumber(L, -1));