Remove unused configurations and packages from laptop setup

- Removed USBGuard configuration and its associated comments from configuration.nix.
- Cleaned up flake.nix by removing unnecessary overlays.
- Updated home.nix to remove references to Helium and Proton, and added Steam.
- Deleted secrets.default.nix and secrets.secrets.yaml files for security reasons.
- Removed Omen laptop specific configuration from omen.nix.
- Deleted vencord.nix as it is no longer needed.

hosts/laptop/flake.nix

@@ -6,8 +6,7 @@
 nixpkgs.lib.nixosSystem {
   modules = [
     {
-      nixpkgs.overlays = [
-      ];
+      nixpkgs.overlays = [];
       _module.args = {inherit inputs;};
     }
     inputs.nixos-hardware.nixosModules.omen-16-n0005ne