torchx/aws: remove unused folder and code (#285)

Summary:
Pull Request resolved: #285

This removes the torchx/aws folder. This isn't used anywhere and doesn't have any tests in OSS and shows up as being an area of low coverage.

{F671944389}

https://app.codecov.io/gh/pytorch/torchx

Reviewed By: kiukchung

Differential Revision: D31801174

fbshipit-source-id: 404d65d612a902cbd8449135b54c5848376a2ff5

Author: d4l3k