harness: Fix docs for stress test functions
harness: Fix docs for stress test functions

notify is not called per buffer, but when the thread is freed.

Comment about serialized events and OOB does not make sense for upstream
events.

https://bugzilla.gnome.org/show_bug.cgi?id=761909

centricular/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,centricular/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,StreamUtils/gstreamer