remove recursion from confirmPivotBlockHeader

[macfarla]

PR description

Remove recursion from confirmPivotBlockHeader in order to simplify.

Fixed Issue(s)

fixes #7109

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• [ ] Considered documentation and added the doc-change-required label to this PR if updates are required.
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Locally, you can run these tests to catch failures early:

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• [ ] integration tests: ./gradlew integrationTest
• [ ] reference tests: ./gradlew ethereum:referenceTests:referenceTests

[macfarla]

looks like the simplest thing is not entirely working -

[macfarla]

Actually the full burn-in looks much the same as current RC

[macfarla]

closing this since we are going with an alternative approach