Fix breakage with ONNX 1.9.0

Remove the call to onnx.utils.polish_model() because it has been removed
without replacement in ONNX 1.9.0.
This should be fine though, because onnxruntime now actually performs
graph optimizations itself by default:
https://www.onnxruntime.ai/docs/resources/graph-optimizations.html

deface/centerface.py

@@ -34,17 +34,15 @@ def __init__(self, onnx_path=None, in_shape=None, backend='auto'):
             self.net = cv2.dnn.readNetFromONNX(onnx_path)
         elif self.backend == 'onnxrt':
             import onnx
-            import onnx.utils
             import onnxruntime
 
             # Silence warnings about unnecessary bn initializers
             onnxruntime.set_default_logger_severity(3)
 
             static_model = onnx.load(onnx_path)
             dyn_model = self.dynamicize_shapes(static_model)
-            dyn_model = onnx.utils.polish_model(dyn_model)
             self.sess = onnxruntime.InferenceSession(dyn_model.SerializeToString())
-            
+
             preferred_provider = self.sess.get_providers()[0]
             preferred_device = 'GPU' if preferred_provider.startswith('CUDA') else 'CPU'
             # print(f'Running on {preferred_device}.')