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

rpcserver.go

@@ -18,13 +18,14 @@ import (
 	"time"
 
 	"github.com/btcsuite/btcd/blockchain"
-	"github.com/btcsuite/btcd/btcec"
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/ecdsa"
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/btcsuite/btcd/btcutil/psbt"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
-	"github.com/btcsuite/btcutil/psbt"
 	"github.com/btcsuite/btcwallet/waddrmgr"
 	"github.com/btcsuite/btcwallet/wallet/txauthor"
 	"github.com/davecgh/go-spew/spew"
@@ -1239,7 +1240,7 @@ func (r *rpcServer) SendCoins(ctx context.Context,
 	// accidentally tried to send funds to a bare pubkey address. This check is
 	// here to prevent unintended transfers.
 	decodedAddr, _ := hex.DecodeString(in.Addr)
-	_, err = btcec.ParsePubKey(decodedAddr, btcec.S256())
+	_, err = btcec.ParsePubKey(decodedAddr)
 	if err == nil {
 		return nil, fmt.Errorf("cannot send coins to pubkeys")
 	}
@@ -1570,7 +1571,7 @@ func (r *rpcServer) VerifyMessage(ctx context.Context,
 	digest := chainhash.DoubleHashB(in.Msg)
 
 	// RecoverCompact both recovers the pubkey and validates the signature.
-	pubKey, _, err := btcec.RecoverCompact(btcec.S256(), sig, digest)
+	pubKey, _, err := ecdsa.RecoverCompact(sig, digest)
 	if err != nil {
 		return &lnrpc.VerifyMessageResponse{Valid: false}, nil
 	}
@@ -1613,7 +1614,7 @@ func (r *rpcServer) ConnectPeer(ctx context.Context,
 	if err != nil {
 		return nil, err
 	}
-	pubKey, err := btcec.ParsePubKey(pubkeyHex, btcec.S256())
+	pubKey, err := btcec.ParsePubKey(pubkeyHex)
 	if err != nil {
 		return nil, err
 	}
@@ -1682,7 +1683,7 @@ func (r *rpcServer) DisconnectPeer(ctx context.Context,
 	if err != nil {
 		return nil, fmt.Errorf("unable to decode pubkey bytes: %v", err)
 	}
-	peerPubKey, err := btcec.ParsePubKey(pubKeyBytes, btcec.S256())
+	peerPubKey, err := btcec.ParsePubKey(pubKeyBytes)
 	if err != nil {
 		return nil, fmt.Errorf("unable to parse pubkey: %v", err)
 	}
@@ -1749,17 +1750,13 @@ func newFundingShimAssembler(chanPointShim *lnrpc.ChanPointShim, initiator bool,
 
 	// Next we'll parse out the remote party's funding key, as well as our
 	// full key descriptor.
-	remoteKey, err := btcec.ParsePubKey(
-		chanPointShim.RemoteKey, btcec.S256(),
-	)
+	remoteKey, err := btcec.ParsePubKey(chanPointShim.RemoteKey)
 	if err != nil {
 		return nil, err
 	}
 
 	shimKeyDesc := chanPointShim.LocalKey
-	localKey, err := btcec.ParsePubKey(
-		shimKeyDesc.RawKeyBytes, btcec.S256(),
-	)
+	localKey, err := btcec.ParsePubKey(shimKeyDesc.RawKeyBytes)
 	if err != nil {
 		return nil, err
 	}
@@ -1937,7 +1934,7 @@ func (r *rpcServer) parseOpenChannelReq(in *lnrpc.OpenChannelRequest,
 	// Parse the raw bytes of the node key into a pubkey object so we can
 	// easily manipulate it.
 	case len(in.NodePubkey) > 0:
-		nodePubKey, err = btcec.ParsePubKey(in.NodePubkey, btcec.S256())
+		nodePubKey, err = btcec.ParsePubKey(in.NodePubkey)
 		if err != nil {
 			return nil, err
 		}
@@ -1951,7 +1948,7 @@ func (r *rpcServer) parseOpenChannelReq(in *lnrpc.OpenChannelRequest,
 			return nil, err
 		}
 
-		nodePubKey, err = btcec.ParsePubKey(keyBytes, btcec.S256())
+		nodePubKey, err = btcec.ParsePubKey(keyBytes)
 		if err != nil {
 			return nil, err
 		}