Drop non-relevant files for cachi2

[slimreaper35]

Maintainers will complete the following section

• Commit messages are descriptive enough
• Code coverage from testing does not decrease and new code is covered
• Docs updated (if applicable)
• Docs links in the code are still valid (if docs were updated)

Note: if the contribution is external (not from an organization member), the CI
pipeline will not run automatically. After verifying that the CI is safe to run:

• approve GitHub Actions workflows by clicking a button
• approve the Red Hat Trusted App Pipeline container build by commenting /ok-to-test
  (as is the standard for Pipelines as Code)

[brunoapimentel]

There's still a link to the metadata doc we're dropping: https://github.com/containerbuildsystem/cachi2/blob/main/docs/gomod.md?plain=1#L133