Make analyzer happy, remove incorrect instruction (#3181)

Closes https://github.com/flutter/flutter/issues/3149



Closes https://github.com/flutter/flutter/issues/3148

packages/flutter_tools/templates/driver/main_test.dart.tmpl

@@ -3,16 +3,11 @@
 // process or even from another computer. If you are familiar with
 // Selenium/WebDriver for web, Espresso for Android or UI Automation for iOS,
 // this is simply Flutter's version of that.
-//
-// To start the test run the following command from the root of your application
-// package:
-//
-//     flutter drive --target=test_driver/main_test.dart
 
 import 'package:flutter_driver/flutter_driver.dart';
 import 'package:test/test.dart';
 
-main() {
+void main() {
   group('end-to-end test', () {
     FlutterDriver driver;