Don't define volumes in your public Dockerfiles

I had tried to use the sebp/lighttpd container for something before realizing it did this, making it so it can't be used without using volumes, which introduce portability issues and so should only be used when actually needed.

Don't define volumes in your Dockerfiles. Don't do it. That's a client decision.

See bistenes/lighttpd for my volume-free fork.

The real pain came when I found out that docker-compose persists volumes between builds, which is apparently not a bug, it's a feature! despite causing a great deal of wondering why on earth my containers had volumes mounted despite their not being defined anywhere at all.