This update removes obsolete internal code from the Manufacturing app that was no longer used after a previous change. It helps keep the system easier to maintain without changing day-to-day user workflows.

Following #184131, the `_compute_packaging_qtys` method is now useless, and is only called by itself.

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Odoo removed old support code for a deprecated action mechanism that has carried warnings since 2020. This keeps the base platform cleaner and reduces long-term maintenance, with low expected impact because affected customizations have had several years to migrate.

The deprecation warning is set since Odoo 14.0 / June 2020.

Enough water has passed under the bridge since then

An obsolete link between timesheets and planning slots was removed from the Project Timesheet Forecast module. This cleanup reduces unused complexity without changing day-to-day functionality for users.

Before this commit, the slot_id field defined timesheet model is no longer used since the merge of #31996

This commit removes that field since it is deprecated.

task-4600102