Remove no longer needed mempool.clear()
Remove no longer needed mempool.clear()

We don't accept anything in the mempool before we synced to the branch
point, as such this is irrelevant.

bitcoinclassic/bitcoinclassic,bitcoinclassic/bitcoinclassic,zander/bitcoinclassic,bitcoinclassic/bitcoinclassic,zander/bitcoinclassic,zander/bitcoinclassic,bitcoinclassic/bitcoinclassic,zander/bitcoinclassic,zander/bitcoinclassic,zander/bitcoinclassic,bitcoinclassic/bitcoinclassic,bitcoinclassic/bitcoinclassic