Well, you are using a Linux distribution that does use grub by default and many scripts assume that the grub tools are available to make changes that are easy to use for ordinary users.
Now if you change something like the bootloader, which is an essential part of the distro, the only one to blame is you.
An easy way to fix your problem would be to comment out the subprocess.call(['update-grub']) and replace it with pass, to make the function _update_grub do nothing.
def _update_grub(self): #subprocess.call(['update-grub']) passBut you also might want to exchange this function to update the bootloader you are using to pick up an eventual newly generated initial ramdisk.
