[BUG] grubport snippet breaks unified grub.cfg setup of CentOS Stream 9

[nomuranec]

Describe the bug
grubport snippet modifies /boot/efi/EFI/redhat/grub.cfg. Modification is necessary on EFI system with older distros like RHEL7 and RHEL8. However since Fedora 34 and CentOS Stream 9, the file should not be modified as it becomes a step stone to the unified grub.cfg, i.e. /boot/grub2/grub.cfg.

To Reproduce
Steps to reproduce the behavior:

1. Provision CentOS Stream 9 on a system
2. Check /boot/efi/EFI/redhat/grub.cfg

Actual behavior
/boot/efi/EFI/redhat/grub.cfg contains actual boot entries or 'blscfg'.

Expected behavior
/boot/efi/EFI/redhat/grub.cfg should look something like this:

search --no-floppy --set prefix --file /boot/grub2/grub.cfg
set prefix=($prefix)/boot/grub2
configfile $prefix/grub.cfg

Additional context
About unified grub.cfg setup
https://fedoraproject.org/wiki/Changes/UnifyGrubConfig

[StykMartin]

Resolved by #148.