Update README.md to remove certification badge

[davidsandilands]

I have now found out our certification has expired and we are not renewing our membership of the CNCF and will not be able to renew. So removing the badge at this point.

Summary

Provide a detailed description of all the changes present in this pull request.

Additional Context

Add any additional context about the problem here.

• [ ] Root cause and the steps to reproduce. (If applicable)
• [ ] Thought process behind the implementation.

Related Issues (if any)

Mention any related issues or pull requests.

Checklist

• [ ] 🟢 Spec tests.
• [ ] 🟢 Acceptance tests.
• [ ] Manually verified. (For example puppet apply)