nixos auto-upgrade: remove flag when flake

The `--no-build-output` flag that is added by default is only valid
for the old cli, which is not used when flakes are used.

Follow-up to c9daa81eff922d9f77d136cfcff0ea05d40024e0.

Changed files
+2 -3
nixos
modules
+2 -3
nixos/modules/tasks/auto-upgrade.nix
···
'';
}];
-
system.autoUpgrade.flags = [ "--no-build-output" ]
-
++ (if cfg.flake == null then
-
(if cfg.channel == null then
+
system.autoUpgrade.flags = (if cfg.flake == null then
+
[ "--no-build-output" ] ++ (if cfg.channel == null then
[ "--upgrade" ]
else [
"-I"