Remove Symfony 3 compatibility code.

Author: derrabus

EventListener/AbstractSessionListener.php

@@ -55,12 +55,8 @@ public function onKernelRequest(GetResponseEvent $event)
 
         $session = null;
         $request = $event->getRequest();
-        if ($request->hasSession()) {
-            // no-op
-        } elseif (method_exists($request, 'setSessionFactory')) {
+        if (!$request->hasSession()) {
             $request->setSessionFactory(function () { return $this->getSession(); });
-        } elseif ($session = $this->getSession()) {
-            $request->setSession($session);
         }
 
         $session = $session ?? ($this->container && $this->container->has('initialized_session') ? $this->container->get('initialized_session') : null);