Move fetchers into mojo/shell/fetcher

mojo/shell/package_manager/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("//testing/test.gni")
 
 source_set("package_manager") {
   sources = [
     "content_handler_connection.cc",
     "content_handler_connection.h",
     "package_manager_impl.cc",
     "package_manager_impl.h",
   ]
 
   deps = [
-    "//mojo/fetcher",
     "//mojo/shell",
+    "//mojo/shell/fetcher",
     "//mojo/util:filename_util",
   ]
 }
 
 test("unittests") {
   output_name = "mojo_package_manager_unittests"
 
   sources = [
     "capability_filter_content_handler_unittest.cc",
     "content_handler_unittest.cc",
   ]
 
   deps = [
     ":package_manager",
     "//base",
     "//mojo/application/public/cpp",
     "//mojo/shell",
     "//mojo/shell:test_support",
     "//testing/gtest",
     "//third_party/mojo/src/mojo/edk/test:run_all_unittests",
     "//url",
   ]
 }