mojo: first take on removing mojo_main_{chromium,standalone}.

mojo/examples/sample_app/BUILD.gn

 # 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.
 
 import("//mojo/system.gni")
 
 # GYP version: mojo/mojo_examples.gypi:mojo_sample_app
 shared_library("sample_app") {
   output_name = "mojo_sample_app"
 
   deps = [
-    "//mojo/public/cpp/application:main_standalone",
     "//mojo/public/cpp/application:standalone",
     "//mojo/public/cpp/bindings",
-    "//mojo/public/cpp/environment:standalone",
     "//mojo/public/cpp/utility",
     "//mojo/services/public/interfaces/geometry",
     "//mojo/services/public/interfaces/native_viewport",
   ] + mojo_system_for_shared_library + mojo_gles2_for_shared_library
 
   sources = [
     "gles2_client_impl.cc",
     "gles2_client_impl.h",
     "sample_app.cc",
     "spinning_cube.cc",
     "spinning_cube.h"
   ]
 }