[FIX] mail: remove unnecessary modal

this commit removes unnecessary modal that does not let users create
a new users from apps like crm, sale, etc. Now instead of giving requests
that lack email redirectWarning, we open user creation form where user must
set email up.
Reason behind this change is the fact that login is required at the model level,
so the manual checks for this value is not necessary anymore.

task-3262468

closes odoo/odoo#117757

Signed-off-by: Warnon Aurélien (awa) <awa@odoo.com>