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>

remotes/docker/resolver.go

@@ -20,7 +20,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/url"
 	"path"
@@ -359,7 +358,7 @@ func (r *dockerResolver) Resolve(ctx context.Context, ref string) (string, ocisp
 							return "", ocispec.Descriptor{}, err
 						}
 					}
-				} else if _, err := io.Copy(ioutil.Discard, &bodyReader); err != nil {
+				} else if _, err := io.Copy(io.Discard, &bodyReader); err != nil {
 					return "", ocispec.Descriptor{}, err
 				}
 				size = bodyReader.bytesRead