[FIX] website: Remove related website menus on module uninstall

Commit 850e1675eb improved the website.menu creation on module install
(eg: /shop for website_sale).
This commit aims to do the same on module uninstall.

Before this commit:
Uninstalling a website module would uninstall its website.menu (/shop) stored
on the default menu tree.
But the copies of that default menu, on websites, would remains.
Indeed, there is no direct link between the default menus and its copies.

More annoyingly, installing that website module again after uninstalling it
would create a new copy of the default menu, resulting in multiple same menus
on website.

Now, if the menu to be uninstalled is in the default tree menu, we remove all
its copies (the website.menu having that same URL).

Closes #27488, closes #27721

addons/website/models/website.py

@@ -1114,6 +1114,13 @@ class Menu(models.Model):
                 res = super(Menu, self).create(vals)
         return res  # Only one record is returned but multiple could have been created
 
+    @api.multi
+    def unlink(self):
+        default_menu = self.env.ref('website.main_menu', raise_if_not_found=False)
+        for menu in self.filtered(lambda m: default_menu and m.parent_id.id == default_menu.id):
+            self.env['website.menu'].search([('url', '=', menu.url), ('id', '!=', menu.id)]).unlink()
+        return super(Menu, self).unlink()
+
     @api.one
     def _compute_visible(self):
         visible = True

addons/website/tests/test_menu.py

@@ -59,3 +59,11 @@ class TestMenu(common.TransactionCase):
         total_menus = Menu.search_count([])
         Website.create({'name': 'new website'})
         self.assertEqual(total_menus + 4, Menu.search_count([]), "New website's bootstraping should have duplicate default menu tree (Top/Home/Contactus/Sub Default Menu)")
+
+    def test_default_menu_unlink(self):
+        Menu = self.env['website.menu']
+        total_menu_items = Menu.search_count([])
+
+        default_menu = self.env.ref('website.main_menu')
+        default_menu.child_id[0].unlink()
+        self.assertEqual(total_menu_items - 3, Menu.search_count([]), "Deleting a default menu item should delete its 'copies' (same URL) from website's menu trees. In this case, the default child menu and its copies on website 1 and website 2")