watchtower/blob/justice_kit: add BlobType to JusticeKit struct

This is preparation for later commits where the values returned by
member methods will need to be conditioned on the blob type used during
decryption.

watchtower/wtclient/backup_task.go

@@ -194,6 +194,7 @@ func (t *backupTask) craftSessionPayload(
 	// to-local script, and the remote CSV delay.
 	keyRing := t.breachInfo.KeyRing
 	justiceKit := &blob.JusticeKit{
+		BlobType:         t.blobType,
 		SweepAddress:     t.sweepPkScript,
 		RevocationPubKey: toBlobPubKey(keyRing.RevocationKey),
 		LocalDelayPubKey: toBlobPubKey(keyRing.ToLocalKey),
@@ -299,7 +300,7 @@ func (t *backupTask) craftSessionPayload(
 	// Then, we'll encrypt the computed justice kit using the full breach
 	// transaction id, which will allow the tower to recover the contents
 	// after the transaction is seen in the chain or mempool.
-	encBlob, err := justiceKit.Encrypt(key, t.blobType)
+	encBlob, err := justiceKit.Encrypt(key)
 	if err != nil {
 		return hint, nil, err
 	}