Looking for help I found some older threads regarding to this.
For all who are still searching for a solution to get rid of this VAT-Number and adress confirmation:
Simply comment out line 77 and 78 in includes/additionaldomainfields.php.
/*$additionaldomainfields[".de"][] = array("Name" => "Tax ID", "LangVar" => "detldtaxid", "Type" => "text", "Size" => "20", "Default" => "", "Required" => true,);
$additionaldomainfields[".de"][] = array("Name" => "Address Confirmation", "LangVar" => "detldaddressconfirm", "Type" => "tickbox", "Description" => "Please tick to confirm you have a valid German address",);*/
Just wanted to let you know.