* Remove payment requirement for marking expired invoices
Allows to manually mark expired invoices, regardless of registered payments. See dennisreimann/btcpayserver-plugin-lnbank#34 for context, in which BTCPay Server sometimes did not register payments that were received to a LNbank wallet (this got fixed in btcpayserver/BTCPayServer.Lightning#129)
* Refactor conditions for better readability