Remove `torch.contrib._graph_vis` (#24874)
Summary:
This hasn't been edited in a while and doesn't work anymore. Its use
case is also served pretty well by `script_module.code`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24874
Pulled By: driazati
Differential Revision: D16941025
fbshipit-source-id: 11acd05cea5e44eeb1d48188a2de645669b21610
