Audit permissions when adding a user to a service

This is useful information to store for the event, which would be
lost if someone subsequently changed them.

Rather than updating lots of mock assertions, I've replaced them
with a single test / assert at a lower level, which is consistent
with auditing being a non-critical function.

tests/app/main/views/test_register.py

@@ -334,8 +334,6 @@ def test_register_from_email_auth_invite(
     fake_uuid,
     mocker,
 ):
-    mock_audit_event = mocker.patch('app.models.user.create_add_user_to_service_event')
-
     sample_invite['auth_type'] = 'email_auth'
     sample_invite['email_address'] = invite_email_address
     with client.session_transaction() as session:
@@ -373,10 +371,6 @@ def test_register_from_email_auth_invite(
     assert current_user.is_authenticated
     assert mock_add_user_to_service.called
 
-    mock_audit_event.assert_called_once_with(invited_by_id=service_one['users'][0],
-                                             service_id=sample_invite['service'],
-                                             user_id=fake_uuid)
-
     with client.session_transaction() as session:
         # invited user details are still there so they can get added to the service
         assert session['invited_user_id'] == sample_invite['id']