Replace most usages of ioutil with the underlying function

The ioutil functions are deprecated since Go 1.17 and only wrap another
library function. Thus directly call the underlying function.

This commit only mechanically replaces the function calls.

internal/backend/local/local.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"hash"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"syscall"
@@ -209,7 +208,7 @@ func (b *Local) Save(ctx context.Context, h restic.Handle, rd restic.RewindReade
 	return nil
 }
 
-var tempFile = ioutil.TempFile // Overridden by test.
+var tempFile = os.CreateTemp // Overridden by test.
 
 // Load runs fn with a reader that yields the contents of the file at h at the
 // given offset.