revert: "nix: add plymouth"

This reverts commit 84780229db3105ba94eea72fe1f18ea206358382.

nix/modules/boot.nix

@@ -3,8 +3,7 @@
 # theming of grub
 
 {
-  boot = {
+  boot.loader.grub = {
-    loader.grub = {
     theme = pkgs.stdenv.mkDerivation {
       pname = "hyperfluent";
       version = "v1.0.1";
@@ -17,18 +16,4 @@
       installPhase = "cp -r nixos $out";
     };
   };
-
-    initrd.systemd.enable = true;
-
-    plymouth = {
-      enable = true;
-      theme = "rings";
-      themePackages = with pkgs; [
-        # By default we would install all themes
-        (adi1090x-plymouth-themes.override {
-          selected_themes = [ "rings" ];
-        })
-      ];
-    };
-  };
 }