docker: remove description updates when publishing a release

Created by: LawnGnome

We used to update the Docker Hub description for https://hub.docker.com/r/sourcegraph/src-batch-change-volume-workspace on release, but doing so reliably has proven to be difficult, as Docker Hub doesn't provide a reliable API to do this. When it fails, the entire release shows up as red, which is obviously not ideal!

Since this description rarely changes, and the pushes themselves are reliable, this removes the description update and makes it a manual process.