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

mojo/edk/system/dispatcher.cc

Index: mojo/edk/system/dispatcher.cc
diff --git a/mojo/edk/system/dispatcher.cc b/mojo/edk/system/dispatcher.cc
index 07308e61bad6ea3a39fc6b753f5901bbd869193b..7c4d92937794629d1e0970d8e3a1ccf9daa7542c 100644
--- a/mojo/edk/system/dispatcher.cc
+++ b/mojo/edk/system/dispatcher.cc
@@ -525,14 +525,6 @@ bool Dispatcher::EndSerializeAndCloseImplNoLock(
   return false;
 }
 
-bool Dispatcher::IsBusyNoLock() const {
-  mutex_.AssertHeld();
-  DCHECK(!is_closed_);
-  // Most dispatchers support only "atomic" operations, so they are never busy
-  // (in this sense).
-  return false;
-}
-
 void Dispatcher::CloseNoLock() {
   mutex_.AssertHeld();
   DCHECK(!is_closed_);