Work around linker error of multiple definitions of pp::BlockUntilComplete

ppapi/cpp/completion_callback.cc

Index: ppapi/cpp/completion_callback.cc
diff --git a/ppapi/cpp/completion_callback.cc b/ppapi/cpp/completion_callback.cc
deleted file mode 100644
index 982031d1e378ce54184c07f23d278e2fab1e4494..0000000000000000000000000000000000000000
--- a/ppapi/cpp/completion_callback.cc
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright (c) 2011 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 "ppapi/cpp/completion_callback.h"
-
-namespace pp {
-
-CompletionCallback BlockUntilComplete() {
-  return CompletionCallback();
-}
-
-}  // namespace pp