clightning: native database replication

Don't put `clightning.replication` options in
`examples/configuration.nix` until it is more "battle-tested."

pkgs/default.nix

@@ -4,7 +4,7 @@ in
 # Set default values for use without flakes
 { pkgs ? import <nixpkgs> { config = {}; overlays = []; }
 , pkgsUnstable ? import nixpkgsPinned.nixpkgs-unstable {
-    inherit (pkgs) system;
+    inherit (pkgs.stdenv) system;
     config = {};
     overlays = [];
   }