No --vnet=[0/1] flag in inference/predict_simple.py

[davidkvcs]

The guide says to use the line

python inference/predict_simple.py -i INPUT_FOLDER -o OUTPUT_FOLDER -t TaskXX_MY_DATASET -tr nnUNetTrainer -m [3d_fullres/3d_lowres] --vnet=[0/1]
in order to do inference.

But the --vnet flag does not exist for inference/predict_simple.py.

So the scripts will crash if used in this way.