refactor(natu): remove custom Nix linter

src/skills/style/nix/SKILL.md

@@ -12,10 +12,7 @@ After editing Nix files, run:
 
 ```bash
 nix run .#fix
-bazel run //src/natu:natu -- <modified-nix-paths>
 ```
 
-Pass every modified Nix path to Natu.
-
-Finish when both commands succeed and the Nix change follows the loaded rules.
-If a command fails, report the failure.
+Finish when the command succeeds and the Nix change follows the loaded rules.
+If the command fails, report the failure.