When the custom batch serialization was being used instead of RLP, a
transaction being sent to `address(0)` was not allowed because that
meant that it was a contract creation because there is no abi encoding
for `nil`. To prevent collisions, transactions sent via RPC to
`address(0)` were banned. Now the RLP transactions are being used, this
check can be removed. It helps to reduce the diff from upstream geth.