Remove all blimp engine code

blimp/engine/app/ui/blimp_window_parenting_client.cc

-// 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 "blimp/engine/app/ui/blimp_window_parenting_client.h"
-
-#include "ui/aura/window.h"
-
-namespace blimp {
-namespace engine {
-
-BlimpWindowParentingClient::BlimpWindowParentingClient(
-    aura::Window* root_window)
-    : root_window_(root_window) {
-  aura::client::SetWindowParentingClient(root_window_, this);
-}
-
-BlimpWindowParentingClient::~BlimpWindowParentingClient() {
-  aura::client::SetWindowParentingClient(root_window_, nullptr);
-}
-
-aura::Window* BlimpWindowParentingClient::GetDefaultParent(
-    aura::Window* context,
-    aura::Window* window,
-    const gfx::Rect& bounds) {
-  // Blimp has one root window. Always attach null-parented windows to the root
-  // window.
-  return root_window_;
-}
-
-}  // namespace engine
-}  // namespace blimp