child_process: remove redundant condition

There is no need to check `flowing` since `resume` does
nothing when `flowing` is already true.

PR-URL: #511
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>

lib/child_process.js

@@ -1057,8 +1057,7 @@ util.inherits(ChildProcess, EventEmitter);
 function flushStdio(subprocess) {
   if (subprocess.stdio == null) return;
   subprocess.stdio.forEach(function(stream, fd, stdio) {
-    if (!stream || !stream.readable || stream._consuming ||
-        stream._readableState.flowing)
+    if (!stream || !stream.readable || stream._consuming)
       return;
     stream.resume();
   });