Revert "Check if a stream has a valid fd before read_start"

uv_stream_t.fd is a private field which exists only on unix.
This reverts commit 8d5c120.

src/stream_wrap.cc

@@ -132,10 +132,6 @@ Handle<Value> StreamWrap::ReadStart(const Arguments& args) {
 
   UNWRAP(StreamWrap)
 
-  // Probably the user did .pause() and then an immediate .resume()
-  // before the fd had been set up. Don't even try to set up.
-  if (wrap->stream_->fd < 0) return scope.Close(Integer::New(1));
-
   bool ipc_pipe = wrap->stream_->type == UV_NAMED_PIPE &&
                   ((uv_pipe_t*)wrap->stream_)->ipc;
   int r;