Remove use of std::function from Mojo internals

mojo/edk/system/data_pipe_producer_dispatcher.cc

Index: mojo/edk/system/data_pipe_producer_dispatcher.cc
diff --git a/mojo/edk/system/data_pipe_producer_dispatcher.cc b/mojo/edk/system/data_pipe_producer_dispatcher.cc
index 8273c14d18fc144adf2255568922ffd1f0413565..8c1993aa5d36dd474b904eabeb5f1169465e5a9c 100644
--- a/mojo/edk/system/data_pipe_producer_dispatcher.cc
+++ b/mojo/edk/system/data_pipe_producer_dispatcher.cc
@@ -504,8 +504,8 @@ void DataPipeProducerDispatcher::UpdateSignalsStateNoLock() {
   } else if (rv == ports::OK && port_status.has_messages && !in_transit_) {
     ports::ScopedMessage message;
     do {
-      int rv = node_controller_->node()->GetMessageIf(control_port_, nullptr,
-                                                      &message);
+      int rv = node_controller_->node()->GetMessage(
+          control_port_, &message, nullptr);
       if (rv != ports::OK)
         peer_closed_ = true;
       if (message) {