Issue #3228656 by bradjones1, Spokje: Remove outdated @todo in HtmlResponseAttachmentsProcessor

core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php

@@ -112,10 +112,7 @@ public function __construct(AssetResolverInterface $asset_resolver, ConfigFactor
    * {@inheritdoc}
    */
   public function processAttachments(AttachmentsInterface $response) {
-    // @todo Convert to assertion once https://www.drupal.org/node/2408013 lands
-    if (!$response instanceof HtmlResponse) {
-      throw new \InvalidArgumentException('\Drupal\Core\Render\HtmlResponse instance expected.');
-    }
+    assert($response instanceof HtmlResponse);
 
     // First, render the actual placeholders; this may cause additional
     // attachments to be added to the response, which the attachment