How to hide block titles in certain regions

I used to the following in a drupal 7 theme.

function mytheme_preprocess_block(&$variables) {
    // Add class to block titles.
    $variables['title_attributes_array']['class'][] = 'block-title';
    if ($variables['block']->region == 'header_top' ||
        $variables['block']->region == 'search_box' ||
        $variables['block']->region == 'footer') {
        $variables['title_attributes_array']['class'][] = 'element-invisible';
    }
}

Tried several alternatives including preprocess_layout without any success.