Assuming this stuff isn't actually used much; disable it by default
and avoid allocating and tracking the task_delay_info structure.

taskstats is changed to still report the regular sched and sched_info
and only skip the missing task_delay_info fields instead of not
reporting anything.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NIngo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210505111525.308018373@infradead.org