[ONNX] Remove unused patching methods (#83006)
### Description
<!-- What did you change and why was it needed? -->
Remove unused patching methods:
- `torch._C.Graph.constant`
- unpatch `torch._C.Node.__getitem__` and move the helper function to `symbolic_helper`
Add typing annotations
### Issue
<!-- Link to Issue ticket or RFP -->
#76254
### Testing
<!-- How did you test your change? -->
Unit tested
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83006
Approved by: https://github.com/BowenBao
