Update UE to remove MessageLoop::current()->WatchFileDescriptor.

MessageLoop::current()->WatchFileDescriptor is deprecated. And UE should
remove usages of it.

Test: mma && unittest
Change-Id: Ib1ef2e6b6a38ad2a8d07b78bcd72fdb3b7f82226
diff --git a/common/subprocess.h b/common/subprocess.h
index f1b9f1f..432d4cb 100644
--- a/common/subprocess.h
+++ b/common/subprocess.h
@@ -123,12 +123,8 @@
 
     // These are used to monitor the stdout of the running process, including
     // the stderr if it was redirected.
-#ifdef __ANDROID__
-    brillo::MessageLoop::TaskId stdout_task_id{
-        brillo::MessageLoop::kTaskIdNull};
-#else
     std::unique_ptr<base::FileDescriptorWatcher::Controller> stdout_controller;
-#endif  // __ANDROID__
+
     int stdout_fd{-1};
     std::string stdout;
   };