[FIX] mail_plugin: do not enrich blacklisted domains

Bug
===
Currently, we try to enrich the domains even if they are in the
`_MAIL_DOMAIN_BLACKLIST`. IAP always return a "missing data" error
because it can't enrich "gmail.com", etc except for "odoo.com". In that
case the enrichment is successful, but because the domain is
blacklisted, we use the entire email to find the company (and so it
will create a company for each odoo.com email addresses).

The test that was removed was wrong. It works because we mocked the
enrichment response, but in practice it will always return a missing
data error.

Task-3050230

closes odoo/odoo#104621

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>