cgroup: remove obsolete comment above struct cgroupstats

There's no flag in the delay accounting structure indicates that the task
is waiting on IO since commit 1193829d ("delayacct: cleanup flags in
struct task_delay_info and functions use it"). So remove the comment.
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

include/uapi/linux/cgroupstats.h

@@ -24,8 +24,6 @@
  * basis. This data is shared using taskstats.
  *
  * Most of these states are derived by looking at the task->state value
- * For the nr_io_wait state, a flag in the delay accounting structure
- * indicates that the task is waiting on IO
  *
  * Each member is aligned to a 8 byte boundary.
  */