child_process: remove unnecessary use of inner state

PR-URL: #29358
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/internal/child_process.js

@@ -300,9 +300,7 @@ function flushStdio(subprocess) {
     // TODO(addaleax): This doesn't necessarily account for all the ways in
     // which data can be read from a stream, e.g. being consumed on the
     // native layer directly as a StreamBase.
-    if (!stream || !stream.readable ||
-        stream._readableState.readableListening ||
-        stream[kIsUsedAsStdio]) {
+    if (!stream || !stream.readable || stream[kIsUsedAsStdio]) {
       continue;
     }
     stream.resume();