cgroup: remove useless code in cgroup_write_event_control()

eventfd_poll() never returns POLLHUP.
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup.c

@@ -3937,12 +3937,6 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
 	if (ret)
 		goto fail;
 
-	if (efile->f_op->poll(efile, &event->pt) & POLLHUP) {
-		event->cft->unregister_event(cgrp, event->cft, event->eventfd);
-		ret = 0;
-		goto fail;
-	}
-
 	/*
 	 * Events should be removed after rmdir of cgroup directory, but before
 	 * destroying subsystem state objects. Let's take reference to cgroup