e11sync-static: do not use intermediate shell

pkgs/e11sync-static.nix

@@ -6,7 +6,6 @@
   brotli,
   findutils,
   dart-sass,
-  gawk,
 }: let
   self = stdenv.mkDerivation {
     name = "e11sync-static";
@@ -15,9 +14,6 @@
       python3Packages.django
       python3Packages.django-compressor
       dart-sass
-      zopfli
-      brotli
-      gawk
       findutils
     ];
     patchPhase = ''patchShebangs --build manage.py'';
@@ -32,8 +28,8 @@
           -name '*.css' -or \
           -name '*.js' -or \
           -name '*.svg' | \
-          awk '{print "zopfli \""$0"\"";print "brotli \""$0"\""}' | \
-          xargs -P''$(nproc) -I{} $SHELL -c {}
+          tee >(xargs -n1 -P''$(nproc) ${zopfli}/bin/zopfli) | \
+          xargs -n1 -P''$(nproc) ${brotli}/bin/brotli
     '';
     installPhase = ''mv static $out'';