Since the systemd boot counting PR was merged, dashes in specialisation
names cause issues when installing the boot loader entries, since dashes
are also used as separator for the different components of the file name
of the boot loader entries on disk.
The assertion avoids this footgun which is pretty annoying to recover
from.
these changes were generated with nixq 0.0.2, by running
nixq ">> lib.mdDoc[remove] Argument[keep]" --batchmode nixos/**.nix
nixq ">> mdDoc[remove] Argument[keep]" --batchmode nixos/**.nix
nixq ">> Inherit >> mdDoc[remove]" --batchmode nixos/**.nix
two mentions of the mdDoc function remain in nixos/, both of which
are inside of comments.
Since lib.mdDoc is already defined as just id, this commit is a no-op as
far as Nix (and the built manual) is concerned.
