nixos/installer/plasma6: trim closure (#418266)

nixos/modules/installer/cd-dvd/installation-cd-graphical-calamares-plasma6.nix

···
     pkgs.maliit-keyboard
   ];
 
+  environment.plasma6.excludePackages = [
+    # Optional wallpapers that add 126 MiB to the graphical installer
+    # closure. They will still need to be downloaded when installing a
+    # Plasma system, though.
+    pkgs.kdePackages.plasma-workspace-wallpapers
+  ];
+
+  # Avoid bundling an entire MariaDB installation on the ISO.
+  programs.kde-pim.enable = false;
+
   system.activationScripts.installerDesktop =
     let
 

nixos/modules/services/desktop-managers/plasma6.nix

···
           breeze-icons
           breeze-gtk
           ocean-sound-theme
-          plasma-workspace-wallpapers
           pkgs.hicolor-icon-theme # fallback icons
           qqc2-breeze-style
           qqc2-desktop-style
···
           [
             aurorae
             plasma-browser-integration
+            plasma-workspace-wallpapers
             konsole
             kwin-x11
             (lib.getBin qttools) # Expose qdbus in PATH