Remove unnecessary string copy.
Remove unnecessary string copy.

Strings are immutable, so instead of copying as a new variable (like
how was needed when receiving byte slices), just pass the marshaled
JSON string to the notification processing code.

btcsuite/btcwallet,Roasbeef/btcwallet,jrick/dcrwallet,synrg-labs/btcwallet,jrick/btcwallet,synrg-labs/btcwallet,decred/dcrwallet,Roasbeef/btcwallet,jrick/btcwallet,Stash-Crypto/btcwallet,Stash-Crypto/btcwallet,btcsuite/btcwallet,decred/dcrwallet,jrick/dcrwallet