traced_probes: "sched" atrace group: remove sched_wakeup

Usually redundant if we have sched_waking, but can still be re-enabled
explicitly if necessary.

I've decided to keep the atrace binary as-is, since:
* I don't think it's used in scenarios where trace size greatly matters, so the
  change in behaviour doesn't seem worth it.
* it doesn't have a way to explicitly enable the event.

Change-Id: I327117c217359098c143f588581d461fc021c6b3