Avoid duplicated emails in party and contact mechanism default email

issue11506
review427221003
(grafted from bc92627b6fc9be0da22fb51ba50ee7db4f228fe3)

--HG--
branch : 6.0

ir.py

@@ -51,6 +51,18 @@ class EmailTemplate(metaclass=PoolMeta):
         return super().email_models() + [
             'party.party', 'party.contact_mechanism']
 
+    @classmethod
+    def _get_default_exclude(cls, record):
+        pool = Pool()
+        Party = pool.get('party.party')
+        ContactMechanism = pool.get('party.contact_mechanism')
+        exclude = super()._get_default_exclude(record)
+        if isinstance(record, Party):
+            exclude.append('contact_mechanisms')
+        if isinstance(record, ContactMechanism):
+            exclude.append('party')
+        return exclude
+
     @classmethod
     def _get_address(cls, record):
         pool = Pool()