Merge branch '5.1' into 5.2

* 5.1:
  Fix merge

Author: nicolas-grekas

Tests/ImmutableEventDispatcherTest.php

@@ -13,7 +13,6 @@
 
 use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
-use Symfony\Component\EventDispatcher\Event;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 use Symfony\Component\EventDispatcher\ImmutableEventDispatcher;