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/fs/file_unix.go

@@ -4,7 +4,6 @@
 package fs
 
 import (
-	"io/ioutil"
 	"os"
 	"syscall"
 )
@@ -18,7 +17,7 @@ func fixpath(name string) string {
 // TempFile creates a temporary file which has already been deleted (on
 // supported platforms)
 func TempFile(dir, prefix string) (f *os.File, err error) {
-	f, err = ioutil.TempFile(dir, prefix)
+	f, err = os.CreateTemp(dir, prefix)
 	if err != nil {
 		return nil, err
 	}