Remove no-longer-needed IsBusy...() stuff.

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 69d38f572b1d5a78ea86c4dc8bf4cb799e347efb..febec06c369efdee97341832c3112ebc93e2ddec 100644
--- a/mojo/edk/system/data_pipe_producer_dispatcher.cc
+++ b/mojo/edk/system/data_pipe_producer_dispatcher.cc
@@ -205,10 +205,5 @@ bool DataPipeProducerDispatcher::EndSerializeAndCloseImplNoLock(
   return rv;
 }
 
-bool DataPipeProducerDispatcher::IsBusyNoLock() const {
-  mutex().AssertHeld();
-  return data_pipe_->ProducerIsBusy();
-}
-
 }  // namespace system
 }  // namespace mojo