Revert of Mojo: Eliminate duplicate C API symbols

mojo/public/c/system/set_thunks_for_app.cc

Index: mojo/public/c/system/set_thunks_for_app.cc
diff --git a/mojo/public/c/system/set_thunks_for_app.cc b/mojo/public/c/system/set_thunks_for_app.cc
deleted file mode 100644
index 335cc02b79477bb45f28208414feb74d2f10471c..0000000000000000000000000000000000000000
--- a/mojo/public/c/system/set_thunks_for_app.cc
+++ /dev/null
@@ -1,20 +0,0 @@
-// Copyright 2016 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/public/c/system/thunks.h"
-
-extern "C" {
-
-#if defined(WIN32)
-#define THUNKS_EXPORT __declspec(dllexport)
-#else
-#define THUNKS_EXPORT __attribute__((visibility("default")))
-#endif
-
-THUNKS_EXPORT size_t MojoSetSystemThunks(
-    const MojoSystemThunks* system_thunks) {
-  return MojoEmbedderSetSystemThunks(system_thunks);
-}
-
-}  // extern "C"