specific submit handler to user form

I have a submit handler to the user form. It redirect the user to a specific page.

use Symfony\Component\HttpFoundation\RedirectResponse as RedirectResponse;

/**
 * @file
 * Primary module hooks for EHESS Propositions 3 module.
 *
 * @DCG
 * This file is no longer required in Drupal 8.
 * @see https://www.drupal.org/node/2217931
 */
function ehess_propositions_3_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'user_form') {
    foreach (array_keys($form['actions']) as $action) {
      if (isset($form['actions'][$action]['#type']) && $form['actions'][$action]['#type'] === 'submit') {
        $form['actions'][$action]['#submit'][] = '_ehess_propositions_3_user_profile_submit';
      }
    }
  }
}

function _ehess_propositions_3_user_profile_submit($form, &$form_state) {
  $response = new RedirectResponse('/admin/content/reglement/');
  $response->send();
}

But the problem is that the submit handler is fired both for user update and user deletion. That block the redirection to "confirm deletion" page of user.

Is there a specific action to updating user form only and not user delete?

$action can be submit and delete. You don't need the foreach loop if you don't want to attach the submit handler to all submit buttons.

Add the handler to the save button directly:

function ehess_propositions_3_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'user_form') {
    $form['actions']['submit']['#submit'][] = '_ehess_propositions_3_user_profile_submit';
  }
}

For the correct way to redirect in a form see https://drupal.stackexchange.com/a/191594/47547