*: remove io/ioutil uses

Close #1764.

cli/server/dump.go

@@ -3,7 +3,6 @@ package server
 import (
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 
@@ -63,7 +62,7 @@ func (d *dump) tryPersist(prefix string, index uint32) error {
 }
 
 func readFile(path string) (*dump, error) {
-	data, err := ioutil.ReadFile(path)
+	data, err := os.ReadFile(path)
 	if err != nil {
 		return nil, err
 	}