Fix Ubuntu 18.04 molecule failures

[jsf9k]

🗣 Description

This pull request adds the netbase package for Ubuntu, which fixes a reproducible error in the converge state of molecule for Ubuntu 18.04. The geerlingguy/docker-ubuntu1804-ansible:latest Docker image is suddenly missing this package, perhaps due to an omission in its base image.

This pull request also cleans up a few files, removing some now-unnecessary cruft.

💭 Motivation and Context

The molecule tests have been reproducibly failing for this repository lately, and this PR fixes that.

This PR resolves (partially) #30.

🧪 Testing

All pre-commit hooks and molecule tests pass.

✅ Checklist

• [x] This PR has an informative and human-readable title.
• [x] Changes are limited to a single goal - eschew scope creep!
• [x] All relevant type-of-change labels have been added.
• [x] I have read the CONTRIBUTING document.
• [x] These code changes follow cisagov code standards.
• [x] All new and existing tests pass.

[jsf9k]

Did you mention anything about this to geerlingguy?

I think the netbase package is missing from the upstream Docker image, and therefore outside his control, but I'll mention @geerlingguy here so he knows.