Correct change made to joints_2d.cpp by 072e403.

scene/2d/joints_2d.cpp

@@ -61,8 +61,6 @@ void Joint2D::_update_joint(bool p_only_free) {
 	if (!body_a || !body_b)
 		return;
 
-	SWAP(body_a, body_b);
-
 	joint = _configure_joint(body_a, body_b);
 
 	if (!joint.is_valid())