Dart: Reorganize files

mojo/dart/apptests/test_apps/pingpong_target/BUILD.gn

 # Copyright 2015 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/public/dart/rules.gni")
 
 dart_pkg("pingpong_target") {
   apps = [ [
         "dart_pingpong_target",
         "lib/main.dart",
       ] ]
   sources = [
     "pubspec.yaml",
   ]
   deps = [
     "//mojo/dart/packages",
     "//mojo/public/dart",
-    "//services/dart/test/dart/service_test_interfaces",
   ]
 }