Delete custom fields in Drupal 7

delete-field.php

/**
 *  Delete field
 */
function mymodule_update_7000() {
  $fields = array(
    'field_myfield1',
    'field_myfield2',
  );
  foreach ($fields as $field) {
    if ($instance = field_info_instance('node', $field, 'page')) {
      field_delete_instance($instance);
    }
  }
  field_purge_batch(count($fields));
}


/**
 * Implements hook_uninstall().
 */
function nexteuropa_map_uninstall() {
  $t = get_t();

  // Deletes the field create by this module.
  $fields = array('map_layers');
  foreach ($fields as $field) {
    if ($instance = field_info_instance('map', $field, 'map')) {
      field_delete_instance($instance);
    }
  }
  field_purge_batch(count($fields));

  drupal_set_message($t('Nexteuropa map has been uninstalled. Map layers field has been deleted.'));
}