Remove old cortextool Docker repository

[jdbaldry]

We have two Docker Hub repositories that have different versions of cortextool Docker images.

• https://hub.docker.com/r/grafana/cortextool/tags
• https://hub.docker.com/r/grafana/cortex-tools/tags

The former has not been updated in two years and I believe we should delete it. We probably need to announce its removal to the CNCF Cortex community.

The latter is still needed until such a time as cortextool is no longer required for Loki.

[jdbaldry]

@grafana/loki-squad Can y'all confirm that you only use the latter cortex-tools repository?

[cstyan]

I can't tell you for sure, but I do see that we have docs that reference the cortextool binary and cortex-tools repo. I don't see where we have any references to the docker image.