The `pos_restaurant_adyen` module, which handled a specific payment feature, has been removed. This functionality has been integrated into the main `point_of_sale` module, streamlining the system. This change improves efficiency and reduces redundancy.

Task: [#4841174](https://www.odoo.com/odoo/1737/tasks/4841174)

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The `pos_restaurant_adyen` module is no longer needed since all its code is related to `set_tip_after_payment` feature, which are now handeled by the `point_of_sale` module. This means that the code from `pos_restaurant_adyen` has to be merged into `pos_adyen`.

This pull request removes redundant code related to `@api.model` decorators within the VoIP module. This cleanup improves the codebase's efficiency and maintainability, addressing a minor technical issue. The change does not impact any user-facing features or functionality.

Task-5391222