szabi/remove-nyc-fields-from-donations-api-and-webhooks-docs

@mjuhasz Could you please have a look? Not much of a change, only removing 2 fields.

Remove the 'Doing business with NYC fields' from the docs. The NYC fields have been superseded by donation custom fields and have been deleted from the database.

For existing customers using these fields custom fields have been created (with the same names - `doing_business_with_nyc_agency` and `doing_business_with_nyc_business_category`), so the API and the webhook are still functional because custom fields are merged into the standard donation fields.