Fix ONNX symbolic for argmin and argmax (#18261)
Summary:
Fix the problem introduced in https://github.com/pytorch/pytorch/pull/17103
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18261
Reviewed By: bddppq
Differential Revision: D14558781
Pulled By: houseroad
fbshipit-source-id: 7bb50072e77d1d7b2a93f4011fa1362f26e9df1c
