remove renovate config and hardcoded image digests

Given that we have a CI schedule rebuilding images on a daily basis, I don't think we actually need renovate in here. The daily pipelines should be sufficient to ensure the images are always up to date in the registry.

I think the kind of renovate configuration used here makes sense for projects where the images are used to deploy and run containers in production somewhere (eg. donate-neo). Then renovate would be useful to ensure the production runtime environment is always up to date, without the need for scheduling daily build+deployment pipelines.

/cc @micah