chore: Drop redundant local-gateway electron postinstall and CI ski... (#31315)

Co-authored-by: n8n-cat-bot[bot] <n8n-cat-bot[bot]@users.noreply.github.com>

.github/actions/setup-nodejs/action.yml

@@ -135,10 +135,6 @@ runs:
         INSTALL_LOG: ${{ runner.temp }}/pnpm-install.log
         SAFE_CHAIN_LOGGING: verbose
         DEBUG: pnpm:*
-        # Skip the Electron binary download triggered by @n8n/local-gateway's
-        # postinstall. CI never runs the Electron app, but the ~150MB binary
-        # fetch fires on every install otherwise.
-        ELECTRON_SKIP_BINARY_DOWNLOAD: 1
       run: |
         set +o pipefail
         timeout --kill-after=30s 300s $INSTALL_COMMAND \

packages/@n8n/local-gateway/package.json

@@ -19,8 +19,7 @@
     "clean": "rimraf dist out .turbo",
     "test": "jest",
     "test:unit": "jest",
-    "test:dev": "jest --watch",
-    "postinstall": "node node_modules/electron/install.js"
+    "test:dev": "jest --watch"
   },
   "dependencies": {
     "@n8n/computer-use": "workspace:*",