Update config.yaml

[toniseibold]

Changes proposed in this Pull Request

Avoid confusion between releases and the config.yaml. In discussion with @lkstrp and @fneum, removing the version variable in the config.yaml avoids having to keep up changing a line of code that is never used in the repo.

Checklist

• [ ] Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• [ ] Data source for new technologies is clearly stated.
• [ ] Newly introduced dependencies are added to environment.yaml (if applicable).
• [ ] A note for the release notes doc/release_notes.rst of the upcoming release is included.
• [x] I consent to the release of this PR's code under the GPLv3 license.