This last minute modification of D4619: https://reviews.bitcoinabc.org/D4619?vs=14737&id=15017#toc is actually necessary to build without the wallet (regardless of the value for ENABLE_BIP70). Digging into my build history, I found I accidentally tested that change with `-DBUILD_WITHWALLET=OFF` instead of the correct `-DBUILD_BITCOIN_WALLET=OFF`