Remove uses of deprecated io/ioutil

The package has been deprecated since Go 1.16: https://go.dev/doc/go1.16#ioutil

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

util/progress/fromreader.go

@@ -2,7 +2,6 @@ package progress
 
 import (
 	"io"
-	"io/ioutil"
 	"time"
 
 	"github.com/moby/buildkit/client"
@@ -24,7 +23,7 @@ func FromReader(w Writer, name string, rc io.ReadCloser) {
 		Vertexes: []*client.Vertex{&vtx},
 	})
 
-	_, err := io.Copy(ioutil.Discard, rc)
+	_, err := io.Copy(io.Discard, rc)
 
 	tm2 := time.Now()
 	vtx2 := vtx

util/progress/printer.go

@@ -3,7 +3,6 @@ package progress
 import (
 	"context"
 	"io"
-	"io/ioutil"
 	"os"
 	"sync"
 
@@ -88,7 +87,7 @@ func NewPrinter(ctx context.Context, w io.Writer, out console.File, mode string)
 		var c console.Console
 		switch mode {
 		case PrinterModeQuiet:
-			w = ioutil.Discard
+			w = io.Discard
 		case PrinterModeAuto, PrinterModeTty:
 			if cons, err := console.ConsoleFromFile(out); err == nil {
 				c = cons