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

channeldb/migration_01_to_11/graph_test.go

@@ -1,13 +1,14 @@
 package migration_01_to_11
 
 import (
+	"encoding/hex"
 	"image/color"
-	"math/big"
 	prand "math/rand"
 	"net"
 	"time"
 
-	"github.com/btcsuite/btcd/btcec"
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/ecdsa"
 	lnwire "github.com/lightningnetwork/lnd/channeldb/migration/lnwire21"
 )
 
@@ -18,12 +19,13 @@ var (
 		"[2001:db8:85a3:0:0:8a2e:370:7334]:80")
 	testAddrs = []net.Addr{testAddr, anotherAddr}
 
-	testSig = &btcec.Signature{
-		R: new(big.Int),
-		S: new(big.Int),
-	}
-	_, _ = testSig.R.SetString("63724406601629180062774974542967536251589935445068131219452686511677818569431", 10)
-	_, _ = testSig.S.SetString("18801056069249825825291287104931333862866033135609736119018462340006816851118", 10)
+	testRBytes, _ = hex.DecodeString("8ce2bc69281ce27da07e6683571319d18e949ddfa2965fb6caa1bf0314f882d7")
+	testSBytes, _ = hex.DecodeString("299105481d63e0f4bc2a88121167221b6700d72a0ead154c03be696a292d24ae")
+	testRScalar   = new(btcec.ModNScalar)
+	testSScalar   = new(btcec.ModNScalar)
+	_             = testRScalar.SetByteSlice(testRBytes)
+	_             = testSScalar.SetByteSlice(testSBytes)
+	testSig       = ecdsa.NewSignature(testRScalar, testSScalar)
 
 	testFeatures = lnwire.NewFeatureVector(nil, nil)
 )
@@ -48,7 +50,7 @@ func createLightningNode(db *DB, priv *btcec.PrivateKey) (*LightningNode, error)
 }
 
 func createTestVertex(db *DB) (*LightningNode, error) {
-	priv, err := btcec.NewPrivateKey(btcec.S256())
+	priv, err := btcec.NewPrivateKey()
 	if err != nil {
 		return nil, err
 	}