Remove unnecessary/unused struct variables.

It was only being used in two places, where it was replaced by a local
constant.

- ReleaseNextThread->WakeupNextThread
- ReleaseAllWaitingThreads->WakeupAllWaitingThreads.

- Separate wait checking from waiting the current thread
- Resume thread when wait_all=true only if all objects are available at once
- Set output to correct wait object index when there are duplicate handles

If a thread was woken up by something, cancel the wakeup timeout.