stream: remove ambiguous code

PR-URL: #29664
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/internal/streams/end-of-stream.js

@@ -69,15 +69,13 @@ function eos(stream, opts, callback) {
   };
 
   const onfinish = () => {
-    writable = false;
     writableFinished = true;
-    if (!readable) callback.call(stream);
+    if (!readable || readableEnded) callback.call(stream);
   };
 
   const onend = () => {
-    readable = false;
     readableEnded = true;
-    if (!writable) callback.call(stream);
+    if (!writable || writableFinished) callback.call(stream);
   };
 
   const onclose = () => {