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>

diff/apply/apply.go

@@ -19,7 +19,6 @@ package apply
 import (
 	"context"
 	"io"
-	"io/ioutil"
 	"time"
 
 	"github.com/containerd/containerd/content"
@@ -99,7 +98,7 @@ func (s *fsApplier) Apply(ctx context.Context, desc ocispec.Descriptor, mounts [
 	}
 
 	// Read any trailing data
-	if _, err := io.Copy(ioutil.Discard, rc); err != nil {
+	if _, err := io.Copy(io.Discard, rc); err != nil {
 		return emptyDesc, err
 	}
 

diff/lcow/lcow.go

@@ -21,7 +21,6 @@ package lcow
 import (
 	"context"
 	"io"
-	"io/ioutil"
 	"os"
 	"path"
 	"runtime"
@@ -166,7 +165,7 @@ func (s windowsLcowDiff) Apply(ctx context.Context, desc ocispec.Descriptor, mou
 	outFile.Close()
 
 	// Read any trailing data
-	if _, err := io.Copy(ioutil.Discard, rc); err != nil {
+	if _, err := io.Copy(io.Discard, rc); err != nil {
 		return emptyDesc, err
 	}
 

diff/stream_windows.go

@@ -21,7 +21,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"sync"
@@ -155,7 +154,7 @@ func (c *binaryProcessor) Close() error {
 }
 
 func getUiqPath() (string, error) {
-	dir, err := ioutil.TempDir("", "")
+	dir, err := os.MkdirTemp("", "")
 	if err != nil {
 		return "", err
 	}

diff/windows/windows.go

@@ -24,7 +24,6 @@ import (
 	"encoding/base64"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"time"
 
 	winio "github.com/Microsoft/go-winio"
@@ -150,7 +149,7 @@ func (s windowsDiff) Apply(ctx context.Context, desc ocispec.Descriptor, mounts
 	}
 
 	// Read any trailing data
-	if _, err := io.Copy(ioutil.Discard, rc); err != nil {
+	if _, err := io.Copy(io.Discard, rc); err != nil {
 		return emptyDesc, err
 	}