Remove docker doc from docs

We now support docker as a native output format, so this doc is out of
date and not useful.

Change-Id: Ib13cfc815a9acb7178bce02a858262d8f3b17c87

doc/source/docker.md

@@ -1,18 +0,0 @@
-Creating Docker Images
-======================
-
-disk-image-create can be used to create a tarball suitable to be imported as a
-docker image. To do this you can change the output of disk-image-create to tar
-with the -t flag and run docker e.g.
-
-```
-disk-image-create -o image -t tar fedora selinux-permissive
-```
-
-Assuming you have docker running and have permission to use it, the tarball can
-be imported into docker and run.
-
-```
-docker import - image:test1 < image.tar
-docker  run -t -i  image:test1 /bin/bash
-```