[tests] Remove deprecated addwitnessaddress call from feature_nulldummy
[tests] Remove deprecated addwitnessaddress call from feature_nulldummy

addwitnessaddress is deprecated. Replace the call to addwitnessaddress
with a call to getnewaddress(address_type='p2sh-segwit')

peercoin/peercoin,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin,DigitalPandacoin/pandacoin,peercoin/peercoin,peercoin/peercoin,DigitalPandacoin/pandacoin