Remove unnecessary ref/unref in iowatcher cb

src/node_io_watcher.cc

@@ -51,9 +51,7 @@ void IOWatcher::Callback(EV_P_ ev_io *w, int revents) {
   argv[0] = Local<Value>::New(revents & EV_READ ? True() : False());
   argv[1] = Local<Value>::New(revents & EV_WRITE ? True() : False());
 
-  io->Ref();
   callback->Call(io->handle_, 2, argv);
-  io->Unref();
 
   if (try_catch.HasCaught()) {
     FatalException(try_catch);