[IMP] mail, *: make mail tests stop relying on this

*: hr_holidays, im_livechat, mail, mail_bot, sms, snailmail, test_mail,
website_livechat, website_slides.

Mail tests are currently relying on this during tests to make env, widget,
data available. We don't wan't to add magic keys to this anymore.

task-2792108

closes odoo/odoo#86559

Related: odoo/enterprise#25341
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>