The Raspberry Pi boot loader was deleting all xx-initrd text files
(which simply contain the path to the actual initrd files) just after
having created them. The code was actually trying to delete real,
obsolete initrd files, which are named <hash>-initrd-initrd (after path
cleaning), but the glob was catching the other files as well.
It boots, but some things still don't work:
1) Installation of DTBs
2) Boot of initrd
Booting still needs a proper config.txt in /boot, which could probably be
managed by NixOS.
