Revert "Move mojo edk into mojo/edk"

mojo/edk/system/entrypoints.h

-// Copyright 2014 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.
-
-#ifndef MOJO_EDK_SYSTEM_ENTRYPOINTS_H_
-#define MOJO_EDK_SYSTEM_ENTRYPOINTS_H_
-
-namespace mojo {
-namespace system {
-
-class Core;
-
-namespace entrypoints {
-
-// Sets the instance of Core to be used by system functions.
-void SetCore(Core* core);
-// Gets the instance of Core to be used by system functions.
-Core* GetCore();
-
-}  // namespace entrypoints
-}  // namepace system
-}  // namespace mojo
-
-#endif  // MOJO_EDK_SYSTEM_ENTRYPOINTS_H_