lnwallet: convert CommitSpendRevoke+CommitSpendNoDelay to use Signer

This commit converts the rearming two commitment spend functions to use
the lnwallet.Signer interface directly rather than manually manage
private keys during the signing process. This commit is in preparation
for implementation of fully automated revoked uncooperative closure
detection and retribution.

lnwallet/script_utils_test.go

@@ -107,11 +107,21 @@ func TestCommitmentSpendValidation(t *testing.T) {
 	}
 
 	// Next, we'll test bob spending with the derived revocation key to
-	// simulate the scenario when alice broadcasts this commitmen
+	// simulate the scenario when alice broadcasts this commitment
 	// transaction after it's been revoked.
 	revokePrivKey := DeriveRevocationPrivKey(bobKeyPriv, revocationPreimage)
-	bobWitnessSpend, err := commitSpendRevoke(delayScript, channelBalance,
-		revokePrivKey, sweepTx)
+	bobRevokeSigner := &mockSigner{revokePrivKey}
+	signDesc = &SignDescriptor{
+		WitnessScript: delayScript,
+		SigHashes:     txscript.NewTxSigHashes(sweepTx),
+		Output: &wire.TxOut{
+			Value: int64(channelBalance),
+		},
+		HashType:   txscript.SigHashAll,
+		InputIndex: 0,
+	}
+	bobWitnessSpend, err := CommitSpendRevoke(bobRevokeSigner, signDesc,
+		sweepTx)
 	if err != nil {
 		t.Fatalf("unable to generate revocation witness: %v", err)
 	}
@@ -128,12 +138,23 @@ func TestCommitmentSpendValidation(t *testing.T) {
 
 	// Finally, we test bob sweeping his output as normal in the case that
 	// alice broadcasts this commitment transaction.
+	bobSigner := &mockSigner{bobKeyPriv}
 	bobScriptp2wkh, err := commitScriptUnencumbered(bobKeyPub)
 	if err != nil {
 		t.Fatalf("unable to create bob p2wkh script: %v", err)
 	}
-	bobRegularSpend, err := commitSpendNoDelay(bobScriptp2wkh,
-		channelBalance, bobKeyPriv, sweepTx)
+	signDesc = &SignDescriptor{
+		WitnessScript: bobScriptp2wkh,
+		SigHashes:     txscript.NewTxSigHashes(sweepTx),
+		Output: &wire.TxOut{
+			Value:    int64(channelBalance),
+			PkScript: bobScriptp2wkh,
+		},
+		HashType:   txscript.SigHashAll,
+		InputIndex: 0,
+	}
+	bobRegularSpend, err := CommitSpendNoDelay(bobSigner, signDesc,
+		sweepTx)
 	if err != nil {
 		t.Fatalf("unable to create bob regular spend: %v", err)
 	}