Remove unused functions in binlog_file.go

[grodowski]

Follow up to #1604, I noticed there's a bunch of currently unused fns. Please close this if these functions are used for ongoing development 🙇

[Copilot]

Pull Request Overview

This pull request removes unused code from the binlog_file.go file, cleaning up dead code that is no longer referenced anywhere in the codebase.

• Removes four unused methods: PreviousFileCoordinatesBy, PreviousFileCoordinates, NextFileCoordinates, and DetachedCoordinates
• Removes the unused detachPattern regex variable and its initialization
• Removes unused imports (errors and regexp) that were only needed by the deleted code

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