paymentrequest: don't show PaymentAck to user
paymentrequest: don't show PaymentAck to user

mainly because the main "merchant" using bip70 is bitpay, and they
are failing all the PaymentAcks due to the tx is using RBF...
no need to confuse users.

follow-up 1686a97ece31aaa1d2c0e6c7042137a5e8a04943

pooler/electrum-ltc,fujicoin/electrum-fjc,spesmilo/electrum,vialectrum/vialectrum,vialectrum/vialectrum,fujicoin/electrum-fjc,spesmilo/electrum,neocogent/electrum,spesmilo/electrum,spesmilo/electrum,neocogent/electrum,wakiyamap/electrum-mona,wakiyamap/electrum-mona,vialectrum/vialectrum,pooler/electrum-ltc,pooler/electrum-ltc,fujicoin/electrum-fjc,wakiyamap/electrum-mona,wakiyamap/electrum-mona,neocogent/electrum,pooler/electrum-ltc