Disable unused docker-pytorch-linux-xenial-py3.6-gcc4.8 job (#47446)
Summary:
The `docker-pytorch-linux-xenial-py3.6-gcc4.8` job is not used for any builds anymore. This PR removes it from CI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47446
Reviewed By: seemethere, samestep
Differential Revision: D24759876
Pulled By: janeyx99
fbshipit-source-id: e7d420fc2c6c7ffa43001d83b449e9ef3070e902
