Enable ESLint no-useless-escape (#23311)

app/javascript/mastodon/features/compose/util/counter.js

@@ -5,5 +5,5 @@ const urlPlaceholder = '$2xxxxxxxxxxxxxxxxxxxxxxx';
 export function countableText(inputText) {
   return inputText
     .replace(urlRegex, urlPlaceholder)
-    .replace(/(^|[^\/\w])@(([a-z0-9_]+)@[a-z0-9\.\-]+[a-z0-9]+)/ig, '$1@$3');
+    .replace(/(^|[^/\w])@(([a-z0-9_]+)@[a-z0-9.-]+[a-z0-9]+)/ig, '$1@$3');
 }