Make the fuchsia mojo/public repo the source of truth.

mojo/public/platform/native/mgl_echo_thunks.c

-// 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/platform/native/mgl_echo_thunks.h"
-
-#include <assert.h>
-
-#include "mojo/public/platform/native/thunk_export.h"
-
-static struct MGLEchoThunks g_echo_thunks = {0};
-
-void MGLEcho(MGLEchoCallback callback, void* closure) {
-  assert(g_echo_thunks.MGLEcho);
-  g_echo_thunks.MGLEcho(callback, closure);
-}
-
-THUNK_EXPORT size_t MojoSetMGLEchoThunks(
-    const struct MGLEchoThunks* mgl_echo_thunks) {
-  if (mgl_echo_thunks->size >= sizeof(g_echo_thunks))
-    g_echo_thunks = *mgl_echo_thunks;
-  return sizeof(g_echo_thunks);
-}