doc: remove confusing signature in fs.md

PR-URL: nodejs#18310
Fixes: nodejs#18305
Refs: nodejs#13424
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

doc/api/fs.md

@@ -2761,9 +2761,8 @@ added: v0.1.31
 -->
 
 * `filename` {string|Buffer}
-* `listener` {Function|undefined} **Default:** `undefined`
-  * `eventType` {string}
-  * `filename` {string|Buffer}
+* `listener` {Function} Optional, a listener previously attached using
+  `fs.watchFile()`
 
 Stop watching for changes on `filename`. If `listener` is specified, only that
 particular listener is removed. Otherwise, *all* listeners are removed,