remove unneccessary nb_classes var

Author: TrojAISec

art/estimators/classification/pytorch.py

@@ -951,7 +951,6 @@ def __repr__(self):
 
     def _make_model_wrapper(self, model: "torch.nn.Module") -> "torch.nn.Module":
         # Try to import PyTorch and create an internal class that acts like a model wrapper extending torch.nn.Module
-        nb_classes = self.nb_classes
         try:
             import torch.nn as nn