Resolve #2756613 "Avoid prefix and"

Closes #2756613

src/Plugin/DisplayVariant/PageBlockDisplayVariant.php

@@ -121,10 +121,6 @@ class PageBlockDisplayVariant extends BlockDisplayVariant implements PluginWizar
         continue;
       }
 
-      $region_name = Html::getClass("block-region-$region");
-      $build[$region]['#prefix'] = '<div class="' . $region_name . '">';
-      $build[$region]['#suffix'] = '</div>';
-
       /** @var \Drupal\Core\Block\BlockPluginInterface[] $blocks */
       $weight = 0;
       foreach ($blocks as $block_id => $block) {