[Openid-specs-fapi] EUIDW-4-Payments update: dropping OAuth

[Anders Rundgren]

Apparently the EUIDW folks finally realized that OAuth is the wrong solution for wallet-based payment authorizations:
https://github.com/digitallabor-berlin/eudiw-sca/blob/ea5db12b59f583f79e3c866896565fa6c93ae2e4/openbanking-r2s.md#payment
That is, a PISP is now just a backend process, technically no different than Stripe & Co, while the wallet only communicates with the Merchant.

My review of the update:
https://github.com/openid/OpenID4VP/issues/180#issuecomment-2203209092

Anders