Removed some superfluous comments and exception declaration in the `convertUserToErpUser` function
within the `User.php` class. These comments were not adding any useful information, and the
exception mentioned was not being thrown, hence their removal.

Related: #103

Customer id was not passed on correctly.
So it happened that the customer id did NOT get into the erp entities.

Related: pcsg/buero#453

fix candyman-gmbh/projektplanung#200

fix brassberg/tickets#222