<?php
use Drupal\field\Entity\FieldStorageConfig;

//include '/Users/alex/dev/xhprof/header.php';

foreach (FieldStorageConfig::loadMultiple() as $field_storage) {
  if ($field_storage->getTargetEntityTypeId() == 'contact_message') {
    $start = microtime(TRUE);
    $id = $field_storage->id();
    $field_storage->delete();
    print "Deleted field storage $id " . round(microtime(TRUE) - $start, 2) . "s\n";
  }
}

//include '/Users/alex/dev/xhprof/footer.php';