Form for billing information
Unfortunately you cannot control billing block fields through UI. There is no such settings since this fields are mandatory for some(infact many) payment processors. This fields are hard coded at https://github.com/civicrm/civicrm-core/blob/master/CRM/Core/Payment.php#L869

You can use buildform hook to remove the second name field. 


  Note: You might get error from some payment processor if second name
  is empty


HTH

Pradeep