[tests] Remove support for bre-BIP31 ping messages
[tests] Remove support for bre-BIP31 ping messages

BIP31 support was added to Bitcoin Core in version 0.6.1. Our test
framework is incompatible with Bitcoin Core versions that old, so remove
all special logic for handling pre-BIP31 pings.

chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin