treewide: Remove all references to SLiM

This fixes the following evaluation error:

  The option `services.xserver.displayManager.slim' can no longer be
  used since it's been removed. The SLIM project is abandoned and their
  last release was in 2013.

  Because of this it poses a security risk to your system.
  Other issues include it not fully supporting systemd and logind
  sessions.
  Please use a different display manager such as LightDM, SDDM, or GDM.
  You can also use the startx module which uses Xinitrc.

Here is the nixpkgs upstream pull request removing SLiM:

  NixOS/nixpkgs#73251

Since I was using a custom theme for SLiM and actually liked the
minimalism, it's probably time to start patching LightDM soon. For now
however, I'll stay with a default LightDM configuration and wait until
I'm getting annoyed :-)

Signed-off-by: aszlig <[email protected]>

Author: aszlig

modules/core/tests.nix

@@ -504,9 +504,6 @@ let
     { check = true;
       path  = ["nixos" "simple"];
     }
-    { check = config.services.xserver.displayManager.slim.enable;
-      path  = ["nixos" "slim"];
-    }
     { check = config.services.snapper.configs != {};
       path  = ["nixos" "snapper"];
     }

modules/module-list.nix

@@ -24,7 +24,6 @@
   ./user/aszlig/programs/taskwarrior
   ./user/aszlig/programs/zsh
   ./user/aszlig/services/i3
-  ./user/aszlig/services/slim
   ./user/aszlig/services/vlock
   ./user/devhell/profiles/base.nix
   ./user/devhell/profiles/packages.nix

modules/user/aszlig/profiles/workstation/default.nix

@@ -60,7 +60,6 @@ in {
     };
 
     vuizvui.user.aszlig.services.i3.enable = true;
-    vuizvui.user.aszlig.services.slim.enable = true;
     vuizvui.user.aszlig.services.vlock.enable = true;
     vuizvui.user.aszlig.services.vlock.user = "aszlig";
 
@@ -160,6 +159,7 @@ in {
         enable = true;
         layout = "dvorak";
 
+        displayManager.lightdm.enable = true;
         displayManager.sessionCommands = ''
           ${pkgs.xorg.xrdb}/bin/xrdb "${pkgs.writeText "xrdb.config" ''
             XTerm*font:                vga