Disable BLS config style in grub

Fedora use "Boot Loader Specification" config style by default. This is
available only in Fedora-patched grub, so it's incompatible with vanilla
grub shipped by dom0.
Disable it, to generate normal boot entries.

QubesOS/qubes-issues#5212

grub/grub.qubes-kernel-vm-support

@@ -5,4 +5,4 @@ if [ -r /usr/share/qubes/marker-vm ] &&
         [ "$(cat /var/lib/qubes/initramfs-updated 2>/dev/null || echo 0)" -ge 1 ]; then
     GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX xen_scrub_pages=0"
 fi
-
+GRUB_ENABLE_BLSCFG=false