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

ui/ozone/platform/dri/BUILD.gn

 # 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.
 
 import("//build/config/linux/pkg_config.gni")
 import("//ui/ozone/ozone.gni")
 
 declare_args() {
   use_mesa_platform_null = false
 }
@@ skipping 17 matching lines @@
     "dri_console_buffer.cc",
     "dri_console_buffer.h",
     "dri_cursor.cc",
     "dri_cursor.h",
     "dri_buffer.cc",
     "dri_buffer.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 111 matching lines @@
       "//ui/events/ozone:events_ozone_layout",
     ]
 
     public_configs = [ ":libgbm" ]
 
     if (use_mesa_platform_null) {
       defines += [ "USE_MESA_PLATFORM_NULL" ]
     }
   }
 }