Revert of [mojo-bindings] Use Watch API instead of MessagePumpMojo

mojo/mojo_variables.gypi

 # 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.
 
 #
 # A set of GYP variables that are shared between various mojo .gyp files.
 #
 {
   'variables': {
     'chromium_code': 1,
@@ skipping 27 matching lines @@
         'mojo_system_for_component': "<(DEPTH)/mojo/mojo_public.gyp:mojo_system_placeholder",
         'mojo_system_for_loadable_module': "<(DEPTH)/mojo/mojo_public.gyp:mojo_system",
       }],
     ],
     'mojo_public_system_unittest_sources': [
       '<(DEPTH)/mojo/public/c/system/tests/core_unittest.cc',
       '<(DEPTH)/mojo/public/c/system/tests/core_unittest_pure_c.c',
       '<(DEPTH)/mojo/public/c/system/tests/macros_unittest.cc',
       '<(DEPTH)/mojo/public/cpp/system/tests/core_unittest.cc',
       '<(DEPTH)/mojo/public/cpp/system/tests/macros_unittest.cc',
-      '<(DEPTH)/mojo/public/cpp/system/tests/watcher_unittest.cc',
     ],
   },
 }