Revert "Replace lightdm with greetd"

This reverts commit f78b6303b9.

modules/gui.nix

@@ -14,14 +14,16 @@ let
 
 in {
   # Display manager
-  services.greetd = {
-    enable = true;
-    settings = rec {
-      initial_session = {
-        command = "${sway}/bin/sway";
-        user = "coolneng";
-      };
-      default_session = initial_session;
+  services.xserver.enable = true;
+  services.xserver.displayManager = {
+    defaultSession = "sway";
+    autoLogin = {
+      enable = true;
+      user = "coolneng";
+    };
+    lightdm = {
+      enable = true;
+      greeter.enable = false;
     };
   };