Remove product_category from events yml

What does this MR do and why?

Since we are getting rid of product_category from metrics (#393366 (closed)) we also want to remove the field from events.

This MR removes product_category from config/events/schema.json. Delete product_category from all events definitions.

There are many changed files, but they all only have the product_category line removed and therefore I think it is possible to review it in one go.

How to set up and validate locally

Do verify that all definitions has been updated you can check out the branch and run grep product_category ee/config/events/* config/events/*

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #402989 (closed)