Combine Two Vector Shapes into One, With One Path (in Sketch App)

(In Sketch, the app.)

I'm trying to create a shape that is symmetrical on the vertical axis.

I made one half of the shape, duplicated it, flipped the duplicate, then grouped the two together into one object using the Union join menu option.

This is almost what I want, except that when displaying the border for the object, the vertical line where I joined the two objects still appears.

Is there a way to combine the two union'ed vector shapes so that one vector path goes around the outside outline?

I believe the equivalent in Photoshop is the Merge Shape Components option. I can't seem to find the equivalent in Sketch.

thank you