/**
 * Form
 */
function mymodule_myform($form, &$form_state) {
  $form['#action'] = 'http://example.com/path';
  $form['#method'] = 'GET';
  $form['#pre_render'][] = 'mymodule_myform_pre_render';
 
  ...
 
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Submit'),
    '#name' => '',
  );
 
  return $form;
}
 
/**
 * Form pre render callback.
 */
function mymodule_myform_pre_render($form) {
  unset($form['form_token']);
  unset($form['form_build_id']);
  unset($form['form_id']);
  return $form;
}

Drupal 7