block_get_blocks_by_region() and block_list() are removed

block_list()

// Drupal 7

$blocks = block_list('sidebar_first');



// Drupal 8
$blocks = entity_load_multiple_by_properties('block', array('theme' => $GLOBALS['theme'], 'region' => 'sidebar_first'));
uasort($blocks, 'Drupal\block\Entity\Block::sort');

Note that the direct approach in D8 let's you also specify the theme, block_list() would only use the current theme.

block_get_blocks_by_region()

The function would load all blocks for a given theme, check access, and render them.
Those are now three different steps.

// Drupal 7
$build = block_get_blocks_by_region('sidebar_first');

// Drupal 8
$blocks = entity_load_multiple_by_properties('block', array('theme' => $GLOBALS['theme'], 'region' => 'sidebar_first'));
uasort($blocks, 'Drupal\block\Entity\Block::sort');
$build = array();
foreach ($blocks as $key => $block) {
  if ($block->access('view')) {
    $build[$key] = entity_view($block, 'block');
  }
}