apple_sdk: clean up unused Libsystem parameter

pkgs/os-specific/darwin/apple-sdk-11.0/apple_sdk.nix

···
   bareFrameworks = (
     lib.mapAttrs framework (import ./frameworks.nix {
       inherit frameworks libs;
-      inherit (pkgs.darwin.apple_sdk_11_0) libnetwork Libsystem;
+      inherit (pkgs.darwin.apple_sdk_11_0) libnetwork;
       libobjc = pkgs.darwin.apple_sdk_11_0.objc4;
     })
   ) // (

pkgs/os-specific/darwin/apple-sdk-11.0/frameworks.nix

···
-{ frameworks, libs, libobjc, Libsystem, libnetwork }: with frameworks; with libs;
+{ frameworks, libs, libobjc, libnetwork }: with frameworks; with libs;
 {
   AGL                              = { inherit Carbon OpenGL; };
   AVFoundation                     = { inherit ApplicationServices AVFCapture AVFCore CoreGraphics simd UniformTypeIdentifiers; };