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

mojo/edk/system/data_pipe_consumer_dispatcher.cc

Index: mojo/edk/system/data_pipe_consumer_dispatcher.cc
diff --git a/mojo/edk/system/data_pipe_consumer_dispatcher.cc b/mojo/edk/system/data_pipe_consumer_dispatcher.cc
index 0c6f7fa9e7647f87545779530403206d3d70e91a..fc14575bd509f515c61ebefe913bc972d1952619 100644
--- a/mojo/edk/system/data_pipe_consumer_dispatcher.cc
+++ b/mojo/edk/system/data_pipe_consumer_dispatcher.cc
@@ -230,10 +230,5 @@ bool DataPipeConsumerDispatcher::EndSerializeAndCloseImplNoLock(
   return rv;
 }
 
-bool DataPipeConsumerDispatcher::IsBusyNoLock() const {
-  mutex().AssertHeld();
-  return data_pipe_->ConsumerIsBusy();
-}
-
 }  // namespace system
 }  // namespace mojo