perf(storagenode): remove backup from append request (#412)

### What this PR does

This PR removes the Backups fields from AppendRequest. Thus, it makes unmarshaling AppendRequest can
be improved.

internal/storagenode/client/log_client.go

@@ -41,12 +41,11 @@ func (c *LogClient) reset(rpcConn *rpc.Conn, _ types.ClusterID, target varlogpb.
 // Append stores data to the log stream specified with the topicID and the logStreamID.
 // The backup indicates the storage nodes that have backup replicas of that log stream.
 // It returns valid GLSN if the append completes successfully.
-func (c *LogClient) Append(ctx context.Context, tpid types.TopicID, lsid types.LogStreamID, data [][]byte, backups ...varlogpb.StorageNode) ([]snpb.AppendResult, error) {
+func (c *LogClient) Append(ctx context.Context, tpid types.TopicID, lsid types.LogStreamID, data [][]byte) ([]snpb.AppendResult, error) {
 	req := &snpb.AppendRequest{
 		TopicID:     tpid,
 		LogStreamID: lsid,
 		Payload:     data,
-		Backups:     backups,
 	}
 	rsp, err := c.rpcClient.Append(ctx, req)
 	if err != nil {

internal/storagenode/testing.go

@@ -132,14 +132,7 @@ func TestAppend(t *testing.T, tpid types.TopicID, lsid types.LogStreamID, dataBa
 	lc, closer := TestNewLogIOClient(t, replicas[0].StorageNodeID, replicas[0].Address)
 	defer closer()
 
-	var backups []varlogpb.StorageNode
-	for _, replica := range replicas[1:] {
-		backups = append(backups, varlogpb.StorageNode{
-			StorageNodeID: replica.StorageNodeID,
-			Address:       replica.Address,
-		})
-	}
-	res, err := lc.Append(context.Background(), tpid, lsid, dataBatch, backups...)
+	res, err := lc.Append(context.Background(), tpid, lsid, dataBatch)
 	assert.NoError(t, err)
 	return res
 }

pkg/varlog/operations.go

@@ -102,13 +102,7 @@ func (v *logImpl) appendTo(ctx context.Context, tpid types.TopicID, lsid types.L
 		return nil, fmt.Errorf("append: %w", err)
 	}
 
-	backup := make([]varlogpb.StorageNode, len(replicas)-1)
-	for i := 0; i < len(replicas)-1; i++ {
-		backup[i].StorageNodeID = replicas[i+1].StorageNodeID
-		backup[i].Address = replicas[i+1].Address
-	}
-
-	res, err := cl.Append(ctx, tpid, lsid, data, backup...)
+	res, err := cl.Append(ctx, tpid, lsid, data)
 	if err != nil {
 		if strings.Contains(err.Error(), "sealed") {
 			err = fmt.Errorf("append: %s: %w", err.Error(), verrors.ErrSealed)

proto/snpb/log_io.proto

@@ -29,7 +29,6 @@ message AppendRequest {
     (gogoproto.customname) = "LogStreamID"
   ];
   repeated bytes payload = 3;
-  repeated varlogpb.StorageNode backups = 4 [(gogoproto.nullable) = false];
 }
 
 message AppendResult {