* util/grub.d/00_header.in: Remove obsolete comment referencing
convert_system_path_to_grub_path().
* util/update-grub.in: Likewise.
* util/update-grub_lib.in (is_path_readable_by_grub): New function.
(convert_system_path_to_grub_path): Add a warning message explaining
that this function is deprecated. Rely on is_path_readable_by_grub()
for the readability checks.
(font_path): Use is_path_readable_by_grub() for the readability
check rather than convert_system_path_to_grub_path().
cab63c95dc