Fix unused variable warning

engine/lua/LuaPhysicsWorld.cpp

@@ -61,7 +61,7 @@ static int physics_world_make_raycast(lua_State* L)
 	LuaStack stack(L);
 
 	PhysicsWorld* world = stack.get_physics_world(1);
-	const char* callback = stack.get_string(2);
+	/* const char* callback = */ stack.get_string(2);
 	int mode = stack.get_int(3);
 	int filter = stack.get_int(4);
 
@@ -77,7 +77,7 @@ static int physics_world_overlap_test(lua_State* L)
 	LuaStack stack(L);
 
 	PhysicsWorld* world = stack.get_physics_world(1);
-	const char* callback = stack.get_string(2);
+	/* const char* callback = */ stack.get_string(2);
 	CollisionType::Enum filter = (CollisionType::Enum) stack.get_int(3);
 	ShapeType::Enum shape_type = (ShapeType::Enum) stack.get_int(4);
 	Vector3 pos = stack.get_vector3(5);