Remove cargoArtifacts from nix flake

I realize now that this wasn't necessary,
and it makes `nix develop` and direnv take much longer than they should.

Author: gefjon

flake.nix

@@ -168,7 +168,6 @@
             packages = [
               rustStable
               rustNightly
-              cargoArtifacts
               pkgs.cargo-insta
             ];
           };