[FIX] base_usability: ir_mail_server avoid breaking Bcc

fix code for smtp_session in inherit of send_email()
Disable module base_mail_sender_bcc that just doesn't work in v16 ; as it's a design problem, I don't plan to fix it.

base_mail_sender_bcc/__manifest__.py

@@ -17,5 +17,8 @@ With this module, when Odoo sends an outgoing email, it adds the sender as Bcc (
     'author': 'Akretion',
     'website': 'https://github.com/akretion/odoo-usability',
     'depends': ['base'],
-    'installable': True,
+    # I set it to False, because this module doesn't work because of send_validated_to in context
+    # cf method _prepare_email_message()
+    # We should now use the module mail_composer_cc_bcc from OCA/social (moved to OCA/mail)
+    'installable': False,
 }