Remove no-longer-needed RouterListener subclass. We can use the Symfony one directly now.

core/lib/Drupal/Core/EventSubscriber/RouterListener.php

-<?php
-
-/**
- * @file
- * Definition of Drupal\Core\EventSubscriber\RouterListener.
- */
-
-namespace Drupal\Core\EventSubscriber;
-
-use Symfony\Component\HttpKernel\HttpKernelInterface;
-use Symfony\Component\HttpKernel\EventListener\RouterListener as SymfonyRouterListener;
-use Symfony\Component\HttpKernel\Event\GetResponseEvent;
-use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
-use Symfony\Component\HttpKernel\Exception\MethodNotAllowedHttpException;
-use Symfony\Component\HttpKernel\Log\LoggerInterface;
-use Symfony\Component\Routing\Matcher\UrlMatcherInterface;
-use Symfony\Component\Routing\Exception\ResourceNotFoundException;
-
-/**
- * Drupal-specific Router listener.
- *
- * This is the bridge from the kernel to the UrlMatcher.
- */
-class RouterListener extends SymfonyRouterListener {
-
-  /**
-   * The Matcher object for this listener.
-   *
-   * This property is private in the base class, so we have to hack around it.
-   *
-   * @var Symfony\Component\Router\Matcher\UrlMatcherInterface
-   */
-  protected $urlMatcher;
-
-  /**
-   * The Logging object for this listener.
-   *
-   * This property is private in the base class, so we have to hack around it.
-   *
-   * @var Symfony\Component\HttpKernel\Log\LoggerInterface
-   */
-  protected $logger;
-
-  public function __construct(UrlMatcherInterface $urlMatcher, LoggerInterface $logger = null) {
-    parent::__construct($urlMatcher, $logger);
-    $this->urlMatcher = $urlMatcher;
-    $this->logger = $logger;
-  }
-
-  /**
-   * {@inheritdoc}
-   *
-   * This method is nearly identical to the parent, except it passes the
-   * $request->attributes->get('system_path') variable to the matcher.
-   * That is where Drupal stores its processed, de-aliased, and sanitized
-   * internal path. We also pass the full request object to the URL Matcher,
-   * since we want attributes to be available to the matcher and to controllers.
-   */
-  public function onKernelRequest(GetResponseEvent $event) {
-    $request = $event->getRequest();
-
-    if (HttpKernelInterface::MASTER_REQUEST === $event->getRequestType()) {
-      $this->urlMatcher->getContext()->fromRequest($request);
-      $this->urlMatcher->setRequest($request);
-    }
-
-    if ($request->attributes->has('_controller')) {
-      // Routing is already done.
-      return;
-    }
-
-    // Add attributes based on the path info (routing).
-    try {
-      $parameters = $this->urlMatcher->match($request->attributes->get('system_path'));
-
-      if (null !== $this->logger) {
-          $this->logger->info(sprintf('Matched route "%s" (parameters: %s)', $parameters['_route'], $this->parametersToString($parameters)));
-      }
-
-      $request->attributes->add($parameters);
-      unset($parameters['_route']);
-      unset($parameters['_controller']);
-      $request->attributes->set('_route_params', $parameters);
-    }
-    catch (ResourceNotFoundException $e) {
-      $message = sprintf('No route found for "%s %s"', $request->getMethod(), $request->getPathInfo());
-
-      throw new NotFoundHttpException($message, $e);
-    }
-    catch (MethodNotAllowedException $e) {
-      $message = sprintf('No route found for "%s %s": Method Not Allowed (Allow: %s)', $request->getMethod(), $request->getPathInfo(), strtoupper(implode(', ', $e->getAllowedMethods())));
-
-      throw new MethodNotAllowedHttpException($e->getAllowedMethods(), $message, $e);
-    }
-  }
-}