Update optional-packages-with-executable-code.md

[DaveVoyles]

As of July 2024 we have deprecated this feature.

I've added a notification at the top of this page to state this and guide users towards docs which illustrate alternative in-app purchase options.

[learn-build-service-prod[bot]]

Learn Build status updates of commit fafc902:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
msix-src/package/optional-packages-with-executable-code.md	:white_check_mark:Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel