Look to the very right of your screen, there should be a button in the middle, press it and all your layers will slide out, press the top one called Global UI, now you should be able to tap and delete your joystick. Make sure you go back to the main layer before you keep editing otherwise you won't be able to tap any of your objects. EDIT: I just branched your project and for a little while I was confused because I couldn't even see it on global layer, when you switch to global zoom all the way out and move up and right, there should be a green box around there, and the joystick you wanna delete is in the box.
