[BUG] Simplify removes local functions from the ONNX model

[aernoudt]

Describe the bug
onnxsim.simplify (version 0.4.35) removes local functions from the model

Model
The issue can be reproduced with following script: testLocalFunction.py.txt

After running onnxsim.simplify the local function MyReshapeFunction is removed from the model and inference fails.
Commenting out lines 69 and 70 makes the inference work.

[aernoudt]

@daquexian any idea what causes this issue?