[FIX] payment_paypal: cny currency removal

## Versions
18.0+

## Issue
No payment is possible with PayPal for invoices expressed in Chinese currency.

## Steps to reproduce
**`account` app required**
- Enable "CNY" currency via `Invoicing / Configuration / Accounting / Currencies`;
- Install, setup and publish PayPal payment provider;
- Move to the Invoice app:
  - Create a new invoice in "CNY" currency for any customer with at least 1 product;
  - Confirm and click on the preview button:
    - Click on the "Pay now" button then "Pay" button of the wizard.

## Cause
"CNY" currency is only supported for Chinese PayPal accounts and for transactions occurring in China.
PayPal says:
> Please note that Chinese Renminbi (CNY) is supported as a payment currency (buyer currency) or settlement currency (holding currency) only for in-country PayPal accounts. If the settlement account is based outside of China, PayPal will convert the funds into the account’s primary currency using the applicable currency conversion rate, which includes a spread or fee.

opw-5071893

closes odoo#232092

Signed-off-by: Antoine Vandevenne (anv) <[email protected]>

Author: barracudapps

addons/payment_paypal/const.py

@@ -2,12 +2,13 @@
 
 # ISO 4217 codes of currencies supported by PayPal
 # See https://developer.paypal.com/docs/reports/reference/paypal-supported-currencies/.
-# Last seen on: 22 September 2022.
+# Last seen on: 04 November 2025.
+
+# CNY removed as it requires in-country PayPal accounts but China mostly uses WeChat and Alipay.
 SUPPORTED_CURRENCIES = (
     'AUD',
     'BRL',
     'CAD',
-    'CNY',
     'CZK',
     'DKK',
     'EUR',