systemPackages: refactor/simplify pkgset import and resolution

pkgs/systemPackages.nix

@@ -1,23 +1,14 @@
 {
   config,
   lib,
-  fn,
   ...
 }:
 with lib;
 let
   cfg = config.machine;
-  pkgsets = fn.lst {
-    path = toString ../pkgsets;
-    fullPath = true;
-  };
 in
 {
-  imports = pkgsets;
-
   environment.systemPackages = flatten (
-    lists.forEach (attrVals (filter (v: !(strings.hasInfix "::" v)) cfg.pkgs) cfg.pkgsets) (
-      v: v.pkgwrap
-    )
+    map (setName: lib.optionals (cfg.pkgsets ? "${setName}") cfg.pkgsets."${setName}".pkgwrap) cfg.pkgs
   );
 }