chore(file source): remove legacy checksum/fingerprinting (#23874)

* Remove legacy checksum/fingerprinting

* Remove unused checkpoints code

* Remove unused import

* Remove scan_fmt

* Add changelog

* Fix changelog

* chore(vdev): apply vdev rust check fixes

* Fully remove BytesChecksum -> FirstLinesChecksum legacy conversion

* Fully remove BytesChecksum

* Fully remove FingerprintStrategy::Checksum

Checksum was already being converted to FirstLinesChecksum, and the `bytes` option, which was the
only difference between it and FirstLinesChecksum, was not used at all (with changes from previous
commits)

* Add helpful comment

* Improve changelog

* Fix compilation

* Update changelog

* Update changelog again

* George Boole

* Fix casing

* Apply suggestions from code review

Co-authored-by: Pavlos Rontidis <pavlos.rontidis@gmail.com>

* Apply suggestions

* Fix markdownlint

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Co-authored-by: Pavlos Rontidis <pavlos.rontidis@gmail.com>