rootfs: Stop building and shipping OPA

[Redent0r]

Merge Checklist

• Followed patch format from upstream recommendation: https://github.com/kata-containers/community/blob/main/CONTRIBUTING.md#patch-format
  • Included a single commit in a given PR - at least unless there are related commits and each makes sense as a change on its own.
• Aware about the PR to be merged using "create a merge commit" rather than "squash and merge" (or similar)
• genPolicy only: Ensured the tool still builds on Windows
• genPolicy only: Updated sample YAMLs' policy annotations, if applicable
• The upstream-missing label (or upstream-not-needed) has been set on the PR.

Summary

Cherry pick from kata-containers#9559

Note: No need to worry about kata-containers@7dd2fde since we don't have the original commit that this commit is trying to revert

Since OPA binary was replaced by the regorus crate, we can finally stop building and shipping the binary.

Test Methodology

[Redent0r]

image build https://dev.azure.com/mariner-org/mariner/_build/results?buildId=560521&view=results

[Redent0r]

https://dev.azure.com/mariner-org/mariner/_build/results?buildId=561904&view=results: Passed all internal e2e, except for 3 that use busybox sample. Verified busybox sample just needs to be updated