Remove the unused BufferedItemWriter.removeOne #8743

Task Summary

The buffered-writer API has a removeOne (Scala) / remove_one (pyamber) method that no production code calls in either language.

Introduced by:

• Add MongoDocument and MemoryDocument #2681 (2024-06-05, "Add MongoDocument and MemoryDocument") added the Scala trait method.
• Add IcebergDocument as one type of the operator result storage #3147 (2025-01-08) added the IcebergTableWriter override.
• Add Storage Layer In Python #3224 (2025-01-30, "Add Storage Layer In Python") mirrored it into pyamber.

Usage removed by #3295 (2025-03-09, "Use Output Ports of an Operator to Write Storage"). It commented out the last live call, writer.removeOne(tupleValue) in the progressive sink's set-snapshot retraction branch, and #3312 later deleted the commented line. The Python remove_one was never used.

It has been dead for eighteen months. What remains is the trait method, the Iceberg implementation in both languages, a no-op override in an amber test stub, and three test cases.

This is a pure deletion with no behaviour change.

Task Type

• Refactor / Cleanup