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

mojo/edk/system/data_pipe_producer_dispatcher.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/edk/system/data_pipe_producer_dispatcher.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "mojo/edk/system/data_pipe.h"
@@ skipping 187 matching lines @@
     size_t* actual_size,
     std::vector<ScopedPlatformHandle>* platform_handles) {
   AssertHasOneRef();  // Only one ref => no need to take the lock.
 
   bool rv = data_pipe_->ProducerEndSerialize(channel, destination, actual_size,
                                              platform_handles);
   data_pipe_ = nullptr;
   return rv;
 }
 
-bool DataPipeProducerDispatcher::IsBusyNoLock() const {
-  mutex().AssertHeld();
-  return data_pipe_->ProducerIsBusy();
-}
-
 }  // namespace system
 }  // namespace mojo