* gnu/system.scm (read-boot-parameters): Remove export.
(read-boot-parameters-file): New variable. Export it.
* guix/scripts/system.scm (profile-boot-parameters): Use
read-boot-parameters-file.
(profile-grub-entries): Use read-boot-parameters-file.
(reinstall-grub): Use read-boot-parameters-file.
(display-system-generation): Use read-boot-parameters-file.