flake: checks: remove unused arguments

flake/checks.nix

@@ -1,10 +1,10 @@
-{ self, inputs, ... }:
+{ inputs, ... }:
 {
   imports = [
     inputs.pre-commit-hooks.flakeModule
   ];
 
-  perSystem = { system, ... }: {
+  perSystem = { ... }: {
     pre-commit = {
       # Add itself to `nix flake check`
       check.enable = true;