tests: funnel: remove state change from stress tests
tests: funnel: remove state change from stress tests

Changing states up and down while buffers are being pushed is not
a valid use case. If a pad is deactivated and reactivated during
a buffer push it is racy with the check of pushed sticky events
and the actual chainfunction call. As it might call the chain
without noticing the peer pad lost its previous sticky events.

https://bugzilla.gnome.org/show_bug.cgi?id=758340

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