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/schema1/converter.go

@@ -23,7 +23,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"strconv"
 	"strings"
 	"sync"
@@ -230,7 +229,7 @@ func (c *Converter) Convert(ctx context.Context, opts ...ConvertOpt) (ocispec.De
 // ReadStripSignature reads in a schema1 manifest and returns a byte array
 // with the "signatures" field stripped
 func ReadStripSignature(schema1Blob io.Reader) ([]byte, error) {
-	b, err := ioutil.ReadAll(io.LimitReader(schema1Blob, manifestSizeLimit)) // limit to 8MB
+	b, err := io.ReadAll(io.LimitReader(schema1Blob, manifestSizeLimit)) // limit to 8MB
 	if err != nil {
 		return nil, err
 	}