Remove inline dockerfile option

Created by: ryan-blunden

I like the intention behind making it super simple to run a container without creating a Dockerfile, but what's the likelihood of this being used in a content change scenario?

The example used in the docs is valid for sure, but couldn't this be achieved by specifying alpine:3 as the image, then supplying the CMD in the example as args instead?

Removing the option to me would simplify things, and allow code to be removed, all without losing functionality (just needs to be done in a different way).