Fix the (reduce)min and (reduce)max ONNX exporting (#15241)
Summary:
max and reducemax are smashed together, we need to support one input case.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15241
Reviewed By: yinghai
Differential Revision: D13473312
Pulled By: houseroad
fbshipit-source-id: 9b8c847286a2631b006ca900271bc0d26574101a
