Remove unused fields

batchid- and voucherno_interface are not used.

They where originally added because someone thought we should enforce
relations in software 

setra_client/models.py

@@ -38,7 +38,6 @@ class Batch(BaseModel):
     period: str
     interface: str
     vouchertype: str
-    batchid_interface: str
 
 
 class Voucher(BaseModel):
@@ -69,7 +68,6 @@ class Transaction(BaseModel):
     discdate: Optional[datetime.date]
     duedate: Optional[datetime.date]
     extinvref: Optional[str]
-    voucherno_interface: Optional[str]
 
 
 class Multi(BaseModel):