Cease excluding ARM64 platforms from Molecule testing where possible

[jsf9k]

🗣 Description

This pull request removes the exclusion of ARM64 platforms from Molecule testing where possible.

💭 Motivation and context

In many cases we no longer need to do this because we are now using native ARM64 GitHub Actions runners.

Resolves #82.
Resolves #83.

🧪 Testing

All automated tests pass.

✅ Pre-approval checklist

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