cleanup(all): stop using deprecated ioutil functions (#381)

Spotted while working on https://github.com/ooni/probe/issues/1417

See https://golang.org/pkg/io/ioutil/

cmd/ooniprobe/internal/autorun/autorun_darwin.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -114,7 +113,7 @@ func (managerDarwin) writePlist() error {
 		return err
 	}
 	log.Infof("exec: writePlist(%s)", plistPath)
-	return ioutil.WriteFile(plistPath, out.Bytes(), 0644)
+	return os.WriteFile(plistPath, out.Bytes(), 0644)
 }
 
 func (managerDarwin) start() error {

cmd/ooniprobe/internal/config/parser.go

@@ -2,7 +2,7 @@ package config
 
 import (
 	"encoding/json"
-	"io/ioutil"
+	"os"
 	"sync"
 
 	"github.com/ooni/probe-cli/v3/cmd/ooniprobe/internal/utils"
@@ -14,7 +14,7 @@ const ConfigVersion = 1
 
 // ReadConfig reads the configuration from the path
 func ReadConfig(path string) (*Config, error) {
-	b, err := ioutil.ReadFile(path)
+	b, err := os.ReadFile(path)
 	if err != nil {
 		return nil, err
 	}
@@ -67,7 +67,7 @@ func (c *Config) Write() error {
 	if c.path == "" {
 		return errors.New("config file path is empty")
 	}
-	if err := ioutil.WriteFile(c.path, configJSON, 0644); err != nil {
+	if err := os.WriteFile(c.path, configJSON, 0644); err != nil {
 		return errors.Wrap(err, "writing config JSON")
 	}
 	return nil

cmd/ooniprobe/internal/config/parser_test.go

@@ -43,11 +43,11 @@ func TestUpdateConfig(t *testing.T) {
 	configPath := tmpFile.Name()
 	defer os.Remove(configPath)
 
-	data, err := ioutil.ReadFile("testdata/config-v0.json")
+	data, err := os.ReadFile("testdata/config-v0.json")
 	if err != nil {
 		t.Error(err)
 	}
-	err = ioutil.WriteFile(configPath, data, 0644)
+	err = os.WriteFile(configPath, data, 0644)
 	if err != nil {
 		t.Error(err)
 	}

cmd/ooniprobe/internal/database/actions.go

@@ -4,7 +4,6 @@ import (
 	"database/sql"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"net/http"
 	"net/url"
 	"os"
@@ -92,7 +91,7 @@ func GetMeasurementJSON(sess sqlbuilder.Database, measurementID int64) (map[stri
 		return nil, errors.New("cannot access measurement file")
 	}
 	measurementFilePath := measurement.Measurement.MeasurementFilePath.String
-	b, err := ioutil.ReadFile(measurementFilePath)
+	b, err := os.ReadFile(measurementFilePath)
 	if err != nil {
 		return nil, err
 	}

cmd/ooniprobe/internal/nettests/nettests_test.go

@@ -3,6 +3,7 @@ package nettests
 import (
 	"context"
 	"io/ioutil"
+	"os"
 	"path"
 	"testing"
 
@@ -11,11 +12,11 @@ import (
 )
 
 func copyfile(source, dest string) error {
-	data, err := ioutil.ReadFile(source)
+	data, err := os.ReadFile(source)
 	if err != nil {
 		return err
 	}
-	return ioutil.WriteFile(dest, data, 0600)
+	return os.WriteFile(dest, data, 0600)
 }
 
 func newOONIProbe(t *testing.T) *ooni.Probe {

cmd/ooniprobe/internal/ooni/ooni.go

@@ -265,7 +265,7 @@ func InitDefaultConfig(home string) (*config.Config, error) {
 	if err != nil {
 		if os.IsNotExist(err) {
 			log.Debugf("writing default config to %s", configPath)
-			if err = ioutil.WriteFile(configPath, defaultConfig, 0644); err != nil {
+			if err = os.WriteFile(configPath, defaultConfig, 0644); err != nil {
 				return nil, err
 			}
 			// If the user did the informed consent procedure in