tests: remove format meta test

This test requires copying the Home Manager checkout to the Nix store,
which seems to require too much memory for the CI jobs. Instead simply
run the format script directly.

(cherry picked from commit 9fe15dc83b)

.github/workflows/test.yml

@@ -18,5 +18,6 @@ jobs:
       with:
         name: nix-community
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
+    - run: ./format -c
     - run: nix-shell . -A install
     - run: nix-shell --pure tests -A run.all

tests/default.nix

@@ -76,7 +76,6 @@ import nmt {
   ] ++ lib.optionals pkgs.stdenv.hostPlatform.isDarwin [
     ./modules/targets-darwin
   ] ++ lib.optionals pkgs.stdenv.hostPlatform.isLinux [
-    ./meta # Suffices to run on one platform.
     ./modules/misc/debug
     ./modules/misc/numlock
     ./modules/misc/pam

tests/meta/default.nix

@@ -1 +0,0 @@
-{ meta-formatting = ./formatting.nix; }

tests/meta/formatting.nix

@@ -1,27 +0,0 @@
-{ config, lib, pkgs, ... }:
-
-with lib;
-
-let
-
-  pinnedNixpkgs = builtins.fetchTarball {
-    url =
-      "https://github.com/NixOS/nixpkgs/archive/05f0934825c2a0750d4888c4735f9420c906b388.tar.gz";
-    sha256 = "1g8c2w0661qn89ajp44znmwfmghbbiygvdzq0rzlvlpdiz28v6gy";
-  };
-
-  pinnedPkgs = import pinnedNixpkgs { };
-
-in {
-  config = {
-    nmt.script = ''
-      PATH="${with pinnedPkgs; lib.makeBinPath [ findutils nixfmt ]}:$PATH"
-      cd ${../..}
-      if ! ${pkgs.runtimeShell} format -c; then
-        fail "${''
-        Expected source code to be formatted with nixfmt but it was not.
-        This error can be resolved by running the './format' in the project root directory.''}"
-      fi
-    '';
-  };
-}