child_process: don't `resume()` created socket

Calling `resume()` on a stream switches it to the old mode which causes
piping stdio from a child process to fail.

Fixes joyent/node#4510.

lib/child_process.js

@@ -65,7 +65,6 @@ function createSocket(pipe, readable) {
   if (readable) {
     s.writable = false;
     s.readable = true;
-    s.resume();
   } else {
     s.writable = true;
     s.readable = false;