[FIX] website_slides: fix datetimeObj.getTime is not a function

HOW TO REPRODUCE
================

- Don't need to login
- From Odoo front-end, go to Courses > Trees, Wood and Gardens >
    Main Trees Categories
- You get the following client error:
    Uncaught Promise > datetimeObj.getTime is not a function

HOW TO SOLVE:
============

Unlike standard JS equivalent, luxon datetime objects don't have a
getTime() function. Replace it by valueOf() function.
Also, remove calls to `DateTime.fromJSDate().formatting_fn()` by
luxon equivalent functions.

see bb09cf76e3

task-3632077

closes odoo/odoo#145573

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/website_slides/static/src/js/slides.js

@@ -2,7 +2,6 @@
 
 import publicWidget from '@web/legacy/js/public/public_widget';
 import { deserializeDateTime } from "@web/core/l10n/dates";
-const { DateTime } = luxon;
 
 publicWidget.registry.websiteSlides = publicWidget.Widget.extend({
     selector: '#wrapwrap',
@@ -20,10 +19,10 @@ publicWidget.registry.websiteSlides = publicWidget.Widget.extend({
             // if presentation 7 days, 24 hours, 60 min, 60 second, 1000 millis old(one week)
             // then return fix formate string else timeago
             var displayStr = '';
-            if (datetimeObj && new Date().getTime() - datetimeObj.getTime() > 7 * 24 * 60 * 60 * 1000) {
-                displayStr = DateTime.fromJSDate(datetimeObj).toFormat('DD');
+            if (datetimeObj && new Date().getTime() - datetimeObj.valueOf() > 7 * 24 * 60 * 60 * 1000) {
+                displayStr = datetimeObj.toFormat('DD');
             } else {
-                displayStr = DateTime.fromJSDate(datetimeObj).toRelative();
+                displayStr = datetimeObj.toRelative();
             }
             $(el).text(displayStr);
         });