Static GRUB config migration does not handle GRUB configs stored in ESP

[travier]

On older Silverblue systems (installed from Silverblue 33 at least), the GRUB config is stored in the ESP instead of /boot.

The migration logic that we have right now is not enough, as it would have to look at this file as well, clean it up, and enable blscfg and maybe also make sure to add the info pointing GRUB to the boot partition to find the boot entries.

See: https://discussion.fedoraproject.org/t/sb42-updates-fail-on-system-with-512mb-boot-128mb-boot-efi/145041/14

And also: #856

[travier]

It looks like blscfg should be enabled by past updates of this file, so we would only have to cleanup the old ostree entries.

[HuijingHei]

Maybe my understanding is not correct, do we need to run grub2-mkconfig to regenerate the new grub.cfg, also enable blscfg as I see the GRUB_ENABLE_BLSCFG=false in /etc/default/grub? Is it necessary to migrate to the static grub config in this case?