auto-allocate-uids not respected

[nrabulinski]

After updating my flake I'm left with an error saying nix-darwin is refusing to delete nixbld user which does not exist on my system because I'm using the auto-allocate-uids feature. That assertion should only apply if that feature is not enabled.

[nrabulinski]

I temporarily worked around the issue by adding

users.knownUsers = lib.mkForce [];
users.knownGroups = lib.mkForce [];

But this only works because no other module appends to those options

[isabelroses]

Take a look at #1335 :)