Update Decred dependencies. (#597)
Update Decred dependencies. (#597)

This also removes the last traces of github.com/btcsuite/golangcrypto
which was previously being pulled in as a dep of a dep.
decred/dcrwallet,decred/dcrwallet,jrick/btcwallet,jrick/dcrwallet,jrick/btcwallet,jrick/dcrwallet