multi: update btcwallet to v0.15.0

Update go.mod to point to latest btcwallet version.

go.mod

@@ -9,7 +9,7 @@ require (
 	github.com/btcsuite/btcd/btcutil/psbt v1.1.3
 	github.com/btcsuite/btcd/chaincfg/chainhash v1.0.1
 	github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f
-	github.com/btcsuite/btcwallet v0.14.1-0.20220412233800-3a6d5d0702b7
+	github.com/btcsuite/btcwallet v0.15.0
 	github.com/btcsuite/btcwallet/wallet/txauthor v1.2.3
 	github.com/btcsuite/btcwallet/wallet/txrules v1.2.0
 	github.com/btcsuite/btcwallet/walletdb v1.4.0