[BUG] Bad node spec for node. Name: Identity_0 OpType: Identity

[jlamperez]

Describe the bug Identity is not supported?

onnxsim model.onnx a.onnx
Your model contains "Tile" ops or/and "ConstantOfShape" ops. Folding these ops can make the simplified model much larger. If it is not expected, please specify "--no-large-tensor" (which will lose some 
optimization chances)
Simplifying...
Traceback (most recent call last):
  File "/usr/local/bin/onnxsim", line 8, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.8/dist-packages/onnxsim/onnx_simplifier.py", line 434, in main
    model_opt, check_ok = simplify(
  File "/usr/local/lib/python3.8/dist-packages/onnxsim/onnx_simplifier.py", line 186, in simplify
    model_opt_bytes = C.simplify(
onnx.onnx_cpp2py_export.checker.ValidationError: No opset import for domain 'Identity_0'