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>

cmd/containerd-stress/density.go

@@ -21,7 +21,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"os/signal"
 	"path/filepath"
@@ -172,7 +171,7 @@ func getMaps(pid int) (map[string]int, error) {
 }
 
 func getppid(pid int) (int, error) {
-	bytes, err := ioutil.ReadFile(filepath.Join("/proc", strconv.Itoa(pid), "stat"))
+	bytes, err := os.ReadFile(filepath.Join("/proc", strconv.Itoa(pid), "stat"))
 	if err != nil {
 		return 0, err
 	}