Task decorator was removed and examples updated

Change-Id: Ie49fe6c2f48a18130d1fd2a3aa5485cd8cee4ed4
Merge "Task decorator was removed and examples updated"
Remove unused utility classes

Removing ThreadGroupExecutor allows to get rid of threading2
dependency. LastFedIter is also not used, so there is no
reason to keep it.

Change-Id: Id396ab59ebf1e2314ef620417d7cac09e1ab8d3b