don't build docker images in CI (#1062)

Author: david-crespo

.github/workflows/docker-image.yml

@@ -49,10 +49,6 @@ This mode of operation will be used in production.
 
 See: xref:docs/how-to-run.adoc[].
 
-== Docker image
-
-This repo includes a Dockerfile that builds an image containing the Nexus and sled agent.  There's a GitHub Actions workflow that builds and publishes the Docker image.  This is used by the https://github.com/oxidecomputer/console/[console] project for prototyping, demoing, and testing.  This is **not** the way Omicron will be deployed on production systems, but it's a useful vehicle for working with it.
-
 == Configuration reference
 
 `nexus` requires a TOML configuration file.  There's an example in