Remove workarounds for Symfony limitations that have been fixed.

core/lib/Drupal/Core/Routing/MatcherDumper.php

@@ -111,12 +111,7 @@ class MatcherDumper implements MatcherDumperInterface {
         'pattern' => $compiled->getPattern(),
         'pattern_outline' => $compiled->getPatternOutline(),
         'number_parts' => $compiled->getNumParts(),
-        // This is only temporary. We need to strip off the compiled route from
-        // route object in order to serialize it. Cloning strips off the
-        // compiled route object. Remove this once
-        // https://github.com/symfony/symfony/pull/4755 is merged and brought
-        // back downstream.
-        'route' => serialize(clone($route)),
+        'route' => serialize($route),
       );
       $insert->values($values);
     }

core/lib/Drupal/Core/Routing/PathMatcher.php

@@ -75,7 +75,7 @@ class PathMatcher implements InitialMatcherInterface {
       }
     }
 
-    if (!count($collection->all())) {
+    if (!count($collection)) {
       throw new ResourceNotFoundException();
     }