Delete ATen mirror stuff (#49028)
Summary:
These files refer to https://travis-ci.org/github/zdevito/ATen and https://github.com/zdevito/ATen which were last updated in 2018 and 2019 respectively. According to zdevito:
> yeah, all of that stuff can be deleted
> was from a time when ATen was a separate repo from pytorch
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49028
Reviewed By: zdevito
Differential Revision: D25401810
Pulled By: samestep
fbshipit-source-id: a8eea7382f91e1aee6f45552645e6d53825fe5a7
