Remove QbftBlockHashing as this is provided by the block hash

[jframe]

PR description

Removes the QbftBlockHashing interface as the same functionality is provided by creating a commitBlock and using its hash. This makes reusing the Qbft library easier too as there no assumptions that the commit hash can be derived from the blockheader and extradata.

Fixed Issue(s)

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• Checked out our contribution guidelines?
• Considered documentation and added the doc-change-required label to this PR if updates are required.
• Considered the changelog and included an update if required.
• For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• spotless: ./gradlew spotlessApply
• unit tests: ./gradlew build
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• integration tests: ./gradlew integrationTest
• reference tests: ./gradlew ethereum:referenceTests:referenceTests

[macfarla]

does it need a changelog entry?

[jframe]

does it need a changelog entry?

Don't think so, it's internal refactoring. And there is nothing documented about the QBFT core module at the moment. So don't think we need to do anything.