Recycling old, unused files

Since the dockerfiles, tests have been migrated to https://github.com/aws/deep-learning-containers

We should clean up the redundant [and hence confusing] files such as
- Dockerfiles
- test/

Inspect the Dockerfiles and test/ directory, then check repository references and the linked deep-learning-containers project to confirm what has migrated. Remove only the redundant files and verify that the remaining toolkit still has no references to them and its relevant checks remain valid.

Written by the indexing model from the issue text.