Remove preprocessing of Dockerfile (.dockerfile)

[rfay]

What happened (or feature request):

The preprocessing of the Dockerfile into .dockerfile is long-since obsolete and unused. Remove it. This has been obsoleted by Docker's ability to do multi-stage builds.

What you expected to happen:

How to reproduce it (as minimally and precisely as possible):

Anything else do we need to know:

Related source links or issues (like source JIRA issue):