Drop use of deprecated io/ioutil package

hack/verify-boilerplate.go

@@ -19,7 +19,6 @@ package main
 import (
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"regexp"
 	"strings"
@@ -146,7 +145,7 @@ func verifyFile(filePath string) error {
 	}
 
 	// read the file
-	b, err := ioutil.ReadFile(filePath)
+	b, err := os.ReadFile(filePath)
 	if err != nil {
 		return err
 	}

validators/cgroup_validator_linux.go

@@ -23,7 +23,6 @@ import (
 	"bufio"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -196,7 +195,7 @@ func (c *CgroupsValidator) getCgroupV2Subsystems(unifiedMountpoint string) ([]st
 	if freezeSupported {
 		subsystems = append(subsystems, "freezer")
 	}
-	data, err := ioutil.ReadFile(filepath.Join(unifiedMountpoint, "cgroup.controllers"))
+	data, err := os.ReadFile(filepath.Join(unifiedMountpoint, "cgroup.controllers"))
 	if err != nil {
 		return nil, err, warn
 	}

validators/kernel_validator.go

@@ -22,7 +22,6 @@ import (
 	"compress/gzip"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -198,7 +197,7 @@ func (k *KernelValidator) getKernelConfigReader() (io.Reader, error) {
 			}
 			// Buffer the whole file, so that we can close the file and unload
 			// kernel config module in this function.
-			b, err := ioutil.ReadFile(path)
+			b, err := os.ReadFile(path)
 			if err != nil {
 				return nil, err
 			}

validators/package_validator_linux.go

@@ -22,7 +22,7 @@ package system
 import (
 	"errors"
 	"fmt"
-	"io/ioutil"
+	"os"
 	"os/exec"
 	"strings"
 
@@ -171,7 +171,7 @@ func getKernelRelease() (string, error) {
 // getOSDistro returns the OS distro of the local machine.
 func getOSDistro() (string, error) {
 	f := "/etc/lsb-release"
-	b, err := ioutil.ReadFile(f)
+	b, err := os.ReadFile(f)
 	if err != nil {
 		return "", fmt.Errorf("failed to read %q: %w", f, err)
 	}