[Ozone-DRI] Remove the extra helper thread and reuse the IO one

ui/ozone/platform/dri/dri.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.
 
 {
   'variables': {
     'internal_ozone_platform_deps': [
       'ozone_platform_dri',
     ],
     'internal_ozone_platform_unittest_deps': [
@@ skipping 37 matching lines @@
         'dri_console_buffer.cc',
         'dri_console_buffer.h',
         'dri_buffer.cc',
         'dri_buffer.h',
         'dri_cursor.cc',
         'dri_cursor.h',
         'dri_gpu_platform_support.cc',
         'dri_gpu_platform_support.h',
         'dri_gpu_platform_support_host.cc',
         'dri_gpu_platform_support_host.h',
-        'dri_helper_thread.cc',
-        'dri_helper_thread.h',
         'dri_surface.cc',
         'dri_surface.h',
         'dri_surface_factory.cc',
         'dri_surface_factory.h',
         'dri_util.cc',
         'dri_util.h',
         'dri_vsync_provider.cc',
         'dri_vsync_provider.h',
         'dri_window.cc',
         'dri_window.h',
@@ skipping 50 matching lines @@
           'hardware_display_controller_unittest.cc',
           'hardware_display_plane_manager_unittest.cc',
           'screen_manager_unittest.cc',
           'test/mock_dri_wrapper.cc',
           'test/mock_dri_wrapper.h',
         ],
       },
     },
   ],
 }