remove nix gc cleaning script and disable keep-outputs instead

sys/profiles/nix/gc.nix

@@ -8,14 +8,4 @@
     options = "--delete-older-than 14d";
   };
   nix.optimise.automatic = true;
-
-  systemd.services.remove-old-nix-gc-roots = let
-    beforeDate = "last month";
-  in {
-    description = "Remove old nix gc roots";
-    script = "exec ${lib.getExe pkgs.findutils} /nix/var/nix/gcroots/auto -not -newermt \"${beforeDate}\" -delete";
-    serviceConfig.Type = "oneshot";
-    before = ["nix-gc.service"];
-    requiredBy = ["nix-gc.service"];
-  };
 }

sys/profiles/nix/nix.nix

@@ -11,7 +11,6 @@
 
     settings = {
       builders-use-substitutes = true;
-      keep-outputs = true;
       keep-derivations = true;
       accept-flake-config = true;
       use-xdg-base-directories = true;