eslint: avoid dev dependencies to reduce closure size

Omitting npm dev dependencies reduces eslint closure size significantly.
This is helpful when using eslint in build pipelines. Following numbers
from `nix path-info --size --closure-size --human-readable` on
aarch64-darwin.

size of:    eslint    closure  remark:
before:  438.3 MiB    2.7 GiB  (includes apple-sdk, compiler, etc.)
after:    10.6 MiB  202.1 MiB  (npmInstallFlags --omit=dev)

pkgs/by-name/es/eslint/package.nix

@@ -31,15 +31,11 @@ buildNpmPackage' rec {
   '';
 
   npmDepsHash = "sha256-F3EUANBvniczR7QxNfo1LlksYPxXt16uqJDFzN6u64Y=";
+  npmInstallFlags = [ "--omit=dev" ];
 
   dontNpmBuild = true;
   dontNpmPrune = true;
 
-  postFixup = ''
-    # Remove broken symlink
-    rm $out/lib/node_modules/eslint/node_modules/eslint-config-eslint
-  '';
-
   meta = {
     description = "Find and fix problems in your JavaScript code";
     homepage = "https://eslint.org";