There are a couple of options. You could override JGoLayeredDigraphAutoLayout.layoutLinks() to not insert the bend points.
There’s no built-in option to the Layered Digraph layout class to do this. The layoutLinks() method of JGoLayeredDigraphAutoLayout occurs at the very end of the layout algorithm and it is the place where the bend points are currently added. As I mentioned in my earlier response, you could override this method to not add the bend points, but it would have no other effect on the layout, so the result would be the same as the results you’re currently getting.