Fix registration payment object migration values

Ghost User
2019-02-13T19:15:59+01:00

#### Previous behaviour
Steps to reproduce:

1. Migrate events
2. Notes in payments like `Event registration Event object (417). Registration: Registration object (8887)`

#### New behaviour
Steps to validate that it works:

1. Migrate events
2. Notes in payments like `Event registration Bowling 2019-02-16 18:00. Registration: Registration object (8887)`