remove js/yarn.nix, as it can be generated at buildtime in the Nix derivation

flake.nix

@@ -36,7 +36,6 @@
           pkgs.writeShellScriptBin "update" ''
             set -eou pipefail
 
-            ${pkgs.yarn2nix}/bin/yarn2nix --lockfile="./js/yarn.lock" > js/yarn.nix
             ${pkgs.mix2nix}/bin/mix2nix ./mix.lock > mix.nix
           '';
 

js/default.nix

@@ -6,10 +6,6 @@ mkYarnPackage rec {
     exclude = [ (filter.matchExt "nix") ];
   };
 
-  packageJSON = ./package.json;
-  yarnLock = ./yarn.lock;
-  yarnNix = ./yarn.nix;
-
   buildPhase = ''
     runHook preBuild