Regression - replace md5 in Block module calls with sha2 hashes

Per Drupal secure coding standards at http://drupal.org/node/845876

md5 and sha1 should not be used any place in Drupal core since 7.0, but are re-introduced in the Block module for 8.x:

core/modules/block/lib/Drupal/block/Plugin/views/display/Block.php
197:      $old_delta = md5($old_delta);
201:      $md5_delta = md5($delta);
202:      $hashes[$md5_delta] = $delta;
203:      $delta = $md5_delta;