[FIX] sale, website_sale: salesperson emails from assignation of online so

- install e-commerce;
- In the website settings, orders followup, set a salesperson;
- By something as a public user;
- Pay the order.

Before this commit:
- 2 emails where create to assign the salesperson to the SO, but these
    emails didn't have a from and the salesperson didn't receive the
    emails.
- 1 email was also create to assign the salesperson to the contact, this
    mail is not necessary.

Now, only one email that assigns the salesperson to the SO is sent,
with a correct from address.

opw-2189683

closes odoo/odoo#44861

X-original-commit: 7c08eb158858b9573d3d84a0b54df0bfca754105
Signed-off-by: Jorge Pinna Puissant (jpp) <jpp@odoo.com>