all: Remove usage of deprecated io/ioutil (#7971)

As of Go 1.16 io/ioutil is deprecated. This replaces usage with the
corresponding functions in package os and package io.

lib/model/testutils_test.go

@@ -8,7 +8,6 @@ package model
 
 import (
 	"context"
-	"io/ioutil"
 	"os"
 	"testing"
 	"time"
@@ -76,7 +75,7 @@ func init() {
 }
 
 func createTmpWrapper(cfg config.Configuration) (config.Wrapper, context.CancelFunc) {
-	tmpFile, err := ioutil.TempFile("", "syncthing-testConfig-")
+	tmpFile, err := os.CreateTemp("", "syncthing-testConfig-")
 	if err != nil {
 		panic(err)
 	}
@@ -215,7 +214,7 @@ func cleanupModelAndRemoveDir(m *testModel, dir string) {
 }
 
 func createTmpDir() string {
-	tmpDir, err := ioutil.TempDir("", "syncthing_testFolder-")
+	tmpDir, err := os.MkdirTemp("", "syncthing_testFolder-")
 	if err != nil {
 		panic("Failed to create temporary testing dir")
 	}