Drupal 7: Delete fields and instancies

gistfile1.txt

/**
 * Delete fields and instancies
 */
function yourmodule_update_7002() {
  $bundles = array (
    'your_contentype' => array(
      'field_yourfield',
    ),
  );

  foreach ($bundles as $bundle => $fields) {
    foreach ($fields as $field) {
      $instance = field_info_instance('node', $field, $bundle);
      field_delete_instance($instance);
    }
  }

  foreach ($bundles as $bundle => $fields) {
    foreach ($fields as $field) {
      field_delete_field($field);
    }
  }
  // Purge all field information.
  field_purge_batch(1000);
}