multi: use btcd's btcec/v2 and btcutil modules

This commit was previously split into the following parts to ease
review:
 - 2d746f68: replace imports
 - 4008f0fd: use ecdsa.Signature
 - 849e33d1: remove btcec.S256()
 - b8f6ebbd: use v2 library correctly
 - fa80bca9: bump go modules

sweep/sweeper.go

@@ -9,9 +9,9 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/davecgh/go-spew/spew"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/input"

sweep/sweeper_test.go

@@ -8,11 +8,11 @@ import (
 	"testing"
 	"time"
 
-	"github.com/btcsuite/btcd/btcec"
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/davecgh/go-spew/spew"
 	"github.com/lightningnetwork/lnd/build"
 	"github.com/lightningnetwork/lnd/input"
@@ -59,7 +59,7 @@ var (
 		0xf8, 0x2e, 0x16, 0x0b, 0xfa, 0x9b, 0x8b, 0x64, 0xf9,
 		0xd4, 0xc0, 0x3f, 0x99, 0x9b, 0x86, 0x43, 0xf6, 0x56,
 		0xb4, 0x12, 0xa3,
-	}, btcec.S256())
+	})
 )
 
 func createTestInput(value int64, witnessType input.WitnessType) input.BaseInput {

sweep/tx_input_set.go

@@ -4,9 +4,9 @@ import (
 	"fmt"
 	"math"
 
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"

sweep/tx_input_set_test.go

@@ -3,8 +3,8 @@ package sweep
 import (
 	"testing"
 
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/stretchr/testify/require"

sweep/txgenerator.go

@@ -6,9 +6,9 @@ import (
 	"strings"
 
 	"github.com/btcsuite/btcd/blockchain"
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"

sweep/walletsweep.go

@@ -4,9 +4,9 @@ import (
 	"fmt"
 	"math"
 
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"

sweep/walletsweep_test.go

@@ -5,10 +5,10 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/lntest/mock"
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"

sweep/weight_estimator.go

@@ -1,9 +1,9 @@
 package sweep
 
 import (
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
 )

sweep/weight_estimator_test.go

@@ -3,10 +3,10 @@ package sweep
 import (
 	"testing"
 
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
 	"github.com/stretchr/testify/require"