Remove ash_unittests/mash_unittests from Windows build targets

mash/example/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")
 
 group("example") {
   testonly = true
 
   deps = [
-    "//ash/mus",
     "//mash/example/views_examples",
     "//mash/example/window_type_launcher",
+    "//mash/simple_wm",
     "//services/service_manager/standalone",
   ]
+
+  if (is_chromeos) {
+    deps += [ "//ash/mus" ]
+  }
 }