This configuration isn't included twice - it's Debian post-installation
script of grub that copy settings to /etc/default/grub, which results in
parameters being duplicated. Leave it as is for now.
Add GRUB_TIMEOUT=0 for faster VM startup.
QubesOS/qubes-issues#2577
Qubes VM require few config options in grub. Ship appropriate
configuration. Debian have grub.d support, so it can be done cleanly.
On Fedora, /etc/default/grub needs to be modified. Still keep the
options in separate file, but include it manually from
/etc/default/grub.
QubesOS/qubes-issues#2577
