Improve ESLint (#4372)

beta/.eslintrc

@@ -1,10 +1,13 @@
 {
   "root": true,
-  "extends": "next",
+  "extends": "next/core-web-vitals",
+  "rules": {
+    "no-unused-vars": "warn"
+  },
   "env": {
     "node": true,
     "commonjs": true,
     "browser": true,
     "es6": true
   }
-}
+}