Remove Composer artifacts

`nix-build override.nix`

nix/composer2nix/override.nix

@@ -0,0 +1,15 @@
+{
+  pkgs ? import <nixpkgs> {
+    inherit system;
+  },
+  system ? builtins.currentSystem,
+}:
+
+let
+  phpPackage = import ./default.nix {
+    inherit pkgs system;
+  };
+in
+phpPackage.override {
+  removeComposerArtifacts = true;
+}