plasma5Packages.ksysguard: remove if !allowAliases

Usually in Nixpkgs, attributes that are remnants of old packages are
only included when aliases are enabled (which they are by default).
This brings plasma5Packages into line with that, and also makes it
easier to check the whole thing evaluates when working on the package
set.

pkgs/desktops/plasma-5/default.nix

@@ -24,9 +24,8 @@ existing packages here and modify it as necessary.
 
 */
 
-{
-  libsForQt5, lib, fetchurl,
-  gconf, gsettings-desktop-schemas
+{ libsForQt5, lib, config, fetchurl
+, gconf, gsettings-desktop-schemas
 }:
 
 let
@@ -123,7 +122,6 @@ let
       kscreen = callPackage ./kscreen.nix {};
       kscreenlocker = callPackage ./kscreenlocker.nix {};
       ksshaskpass = callPackage ./ksshaskpass.nix {};
-      ksysguard = throw "ksysguard has been replaced with plasma-systemmonitor";
       ksystemstats = callPackage ./ksystemstats.nix {};
       kwallet-pam = callPackage ./kwallet-pam.nix {};
       kwayland-integration = callPackage ./kwayland-integration.nix {};
@@ -164,6 +162,8 @@ let
         parachute = callPackage ./3rdparty/kwin/scripts/parachute.nix { };
       };
 
+    } // lib.optionalAttrs (config.allowAliases or true) {
+      ksysguard = throw "ksysguard has been replaced with plasma-systemmonitor";
     };
 in
 lib.makeScope libsForQt5.newScope packages

pkgs/top-level/qt5-packages.nix

@@ -29,7 +29,7 @@ let
     mkPlasma5 = import ../desktops/plasma-5;
     attrs = {
       inherit libsForQt5;
-      inherit (pkgs) lib fetchurl;
+      inherit (pkgs) config lib fetchurl;
       gconf = pkgs.gnome2.GConf;
       inherit (pkgs) gsettings-desktop-schemas;
     };