After 4b128008c5 it took me a while in a
test setup to find out why `root` didn't have the password anymore I
declared in my config.
Because of that I got reminded how the order of preference works for the
password options:
hashedPassword > password > hashedPasswordFile
If the user is new, initialPassword & initialHashedPassword are also
relevant. Also, the override is silent in contrast to any other
conflicting definition in NixOS.
To make this less surprising I decided to warn in such a case -
assertions would probably break too much that technically works as
intended.
Also removed the `initialHashedPassword` for `root`. This would cause a
warning whenever you set something in your own config and a `!` is added
automatically by `users-groups.pl`.
`systemd-sysusers` also seems to implement these precedence rules, so
having the warning for that case also seems useful.