Revert "merged branch fabpot/event-dispatcher-debug (PR #9068)"

This reverts commit 1843b820153ed7efb635c7353a76d1ef75fb4422, reversing
changes made to 510960ed31861e1516bc4fd05f272ca6a36edb2a.
Merge branch '2.2' into 2.3

* 2.2:
  Revert "merged branch fabpot/event-dispatcher-debug (PR #9068)"

Conflicts:
	src/Symfony/Component/HttpKernel/DependencyInjection/RegisterListenersPass.php
	src/Symfony/Component/HttpKernel/Tests/DependencyInjection/RegisterListenersPassTest.php