[FIX] sale_coupon: Coupon mail sent twice

When generating coupons for customers, the email was sent twice due to the values
given on the email_values that is generating a TO (email_to) value (plus using the one given on the template
(recipients_ids))

opw:2574046

closes odoo/odoo#74406

X-original-commit: c99b6ab0a79cf605d78aaa2f9bb00faa192f7fcc
Signed-off-by: Simon Goffin (sig) <sig@openerp.com>
Co-authored-by: simongoffin <sig@odoo.com>

addons/coupon/wizard/coupon_generate.py

@@ -38,7 +38,7 @@ class CouponGenerate(models.TransientModel):
                 del context
                 template = self.env.ref('coupon.mail_template_sale_coupon', raise_if_not_found=False)
                 if template:
-                    email_values = {'email_to': partner.email, 'email_from': self.env.user.email or '', 'subject': subject}
+                    email_values = {'email_from': self.env.user.email or '', 'subject': subject}
                     template.send_mail(coupon.id, email_values=email_values, notif_layout='mail.mail_notification_light')
 
     @api.depends('partners_domain')