nixos: move system.autoUpgrade

This is not installer-specific

nixos/modules/module-list.nix

@@ -64,7 +64,6 @@
   ./i18n/input-method/ibus.nix
   ./i18n/input-method/nabi.nix
   ./i18n/input-method/uim.nix
-  ./installer/tools/auto-upgrade.nix
   ./installer/tools/tools.nix
   ./misc/assertions.nix
   ./misc/crashdump.nix
@@ -802,6 +801,7 @@
   ./system/boot/timesyncd.nix
   ./system/boot/tmp.nix
   ./system/etc/etc.nix
+  ./tasks/auto-upgrade.nix
   ./tasks/bcache.nix
   ./tasks/cpu-freq.nix
   ./tasks/encrypted-devices.nix