This mostly reverts ca23693d28, which
introduced a circular dependency between (gnu system linux-initrd)
and (gnu system mapped-devices).
Reported by Eric Bavier.
* gnu/system/linux-initrd.scm (check-device-initrd-modules): Move to...
* gnu/system/mapped-devices.scm (check-device-initrd-modules): ... here.
* po/guix/POTFILES.in: Adjust accordingly.