As mentioned in #22223, it looks like the deprecation notice about ContainerAwareEventDispatcher is still emerging in some cases.
Step to reproduce:

• install standard edition via create-project symfony/framework-standard-edition foo
• enter project with cd foo
• install bundle via composer require knplabs/knp-paginator-bundle
• enable bundle by adding new Knp\Bundle\PaginatorBundle\KnpPaginatorBundle() in registerBundles of AppKernel

Expected behavior: launching bin/console server:run and navigating to http://127.0.0.1:8000/, no deprecations about ContainerAwareEventDispatcher should be triggered.
Actual behavior: launching bin/console server:run and navigating to http://127.0.0.1:8000/, I see in debug toolbar "User Deprecated: The Symfony\Component\EventDispatcher\ContainerAwareEventDispatcher class is deprecated since version 3.3 and will be removed in 4.0. Use EventDispatcher with closure-proxy injection instead."

The relevant part of source code is in var/cache/dev/appDevDebugProjectContainer.php and it's following

protected function getDebug_EventDispatcherService()
{    
    $this->services['debug.event_dispatcher'] = $instance = new \Symfony\Component\HttpKernel\Debug\TraceableEventDispatcher(new \Symfony\Component\EventDispatcher\ContainerAwareEventDispatcher($this), ${($_ = isset($this->services['debug.stopwatch']) ? $this->services['debug.stopwatch'] : $this->get('debug.stopwatch')) && false ?: '_'}, ${($_ = isset($this->services['monolog.logger.event']) ? $this->services['monolog.logger.event'] : $this->get('monolog.logger.event', ContainerInterface::NULL_ON_INVALID_REFERENCE)) && false ?: '_'});
   // ...
}