Probably on your C drive is a file called 'boot.ini'. I am assuming you have not removed the Ubuntu installation but just wish to 'lose' the screen list?
You will probably need to change the file attributes of this file as it is normally 'read only'. Right click it/properties untick 'read only' and then apply.
Now open it in notepad. Set 'Timeout' to 0 and save file. It should not re-appear on reboot.