Drop experimental.table-writer-merge-operator-enabled config

[arhimondr]

Description

As per title

Motivation and Context

Enabled by default for a very long time. When table_writer_merge_operator_enabled=false partitioned table writes are likely broken.

Impact

table_writer_merge_operator_enabled session property will no longer be available

Test Plan

CI

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• Please make sure your submission complies with our development, formatting, commit message, and attribution guidelines.
• PR description addresses the issue accurately and concisely. If the change is non-trivial, a GitHub Issue is referenced.
• Documented new properties (with its default value), SQL syntax, functions, or other functionality.
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• Adequate tests were added if applicable.
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Release Notes

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== RELEASE NOTES ==

General Changes
* Remove the ``experimental.table-writer-merge-operator-enabled` config property and the ``table_writer_merge_operator_enabled`` session property :pr:`12345`

[arhimondr]

Thank you for the review @yingsu00