refactor: move from io/ioutil to io and os package

The io/ioutil package has been deprecated as of Go 1.16, see
https://golang.org/doc/go1.16#ioutil. This commit replaces the existing
io/ioutil functions with their new definitions in io and os packages.

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

weed/operation/chunked_file.go

@@ -4,9 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"github.com/chrislusf/seaweedfs/weed/pb"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"sort"
 	"sync"
@@ -14,6 +12,7 @@ import (
 	"google.golang.org/grpc"
 
 	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/pb"
 	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
@@ -108,7 +107,7 @@ func readChunkNeedle(fileUrl string, w io.Writer, offset int64, jwt string) (wri
 		return written, err
 	}
 	defer func() {
-		io.Copy(ioutil.Discard, resp.Body)
+		io.Copy(io.Discard, resp.Body)
 		resp.Body.Close()
 	}()