How do I make canvas disappear when crop with cookie cutter.

I have a photo of a round corporate logo which is surrounded by a square box with some background trees etc..  I want the round logo, without any box.  I used the cookie cutter round shape and it deletes all of the trees etc around the round logo.  That's good. Unfortunately, the square canvas is still behind the round box so that when I print it or import it into another program there is a round logo surrounded by a white box.

Is there anyway to crop it or make some sort of adjustment so that the canvas matches the cropped round shape of the logo or otherwise make it disappear so that there is no square box around the logo?