GRUB starting with version 2.02 permits the use of the linux and
initrd commands for both EFI boot in *-efi installations, as
well as 32-bit BIOS boot in i386-pc installations.

This makes the use of the -16 and -efi suffixes for BIOS and EFI
boot obsolete on systems with a modern GRUB installation.

The --with-modern-grub configure flag makes ostree use the
unsuffixed linux/initrd commands when generating a GRUB
configuration, while defaulting to the previous behaviour for
users not wanted this option.