This last minute modification of D4619: https://reviews.bitcoinabc.org/D4619?vs=14737&id=15017#toc broke the 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
This patch fixes the linking such that the build works as expected when the wallet is disabled but BIP70 is still enabled.