Remove zenodo.

[joaander]

Description

Remove zenodo following https://github.com/glotzerlab/signac/pull/903.

Motivation and Context

The signac-flow zenodo record has not been updated since 2019 and there are no plans to start updating it in the future.

Checklist:

• [x] I am familiar with the Contributing Guidelines.
• [x] I agree with the terms of the Contributor Agreement.
• [x] My name is on the list of contributors.
• [ ] The changes introduced by this pull request are covered by existing or newly introduced tests.
• [ ] The package documentation and framework documentation in signac-docs are up to date with these changes.
• [x] I have updated the changelog and added any related issue and pull request numbers for future reference.