Remove scipp and ess specifics

[jokasimr]

Recently some ess specifics were re-added to the repo, see scipp/scippneutron#476 and #192 (comment).

We would like to move those specifics to https://github.com/scipp/ess_template if possible, or at least only include them conditionally, if the repo is a scipp- repo or an ess- repo.

One solution would be to make the workflows jinja templates, and make them render the environment variable settings only if the repo is a scipp repo. However, there are some issues with using templates because they are not picked up well by github bots (please correct / clarify this).