[core] Standardize NPC shop packets

[sruon]

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• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
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• I have read and understood the Contributing Guide and the Code of Conduct.
• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Starting to clean up packets to standardize on this->.
Cleaned up a little bit one of the handler to match the flow of similar handlers.

Steps to test these changes