Submit handler to delete an image style.
function image_style_delete_form_submit($form, &$form_state) {
$style = $form_state['image_style'];
image_style_delete($style, $form_state['values']['replacement']);
drupal_set_message(t('Style %name was deleted.', array(
'%name' => $style
->label(),
)));
$form_state['redirect'] = 'admin/config/media/image-styles';
}