Remove dockerfile: Deckard CI now uses image from kresd CI

ci/Dockerfile

-FROM cznic/ubuntu:16.04
-MAINTAINER Knot DNS <knot-dns@labs.nic.cz>
-
-WORKDIR /root
-CMD ["/bin/bash"]
-
-# knot-resolver used for comparative tests
-# we do not care that much about particular version of resolvers
-# we want to install newer version of Augeas because those from Ubuntu repositories are incredibly slow on some operations
-# context: https://www.redhat.com/archives/augeas-devel/2017-June/msg00000.html
-RUN LC_ALL=C.UTF-8 add-apt-repository ppa:raphink/augeas -y
-RUN apt-get update
-RUN apt-get upgrade -y
-RUN apt-get install -y knot-resolver
-RUN apt-get install -y unbound
-RUN apt-get install -y pdns-recursor
-RUN apt-get install -y python3-augeas python3-pep8 pylint3 python3-pip python3-jinja2 python3-yaml python3-pytest
-# version of dnspython in Ubuntu repository is f**ked up
-RUN pip3 install --upgrade dnspython selenium xvfbwrapper
-

ci/README.rst

+Deckard CI
+==========
+
+For testing with Deckard in Docker use kresd ci image: registry.labs.nic.cz/knot/knot-resolver/ci:debian-stable