[5.3] Fix gatherMiddleware() only unique

[actionm]

For example:

I have a route group with middleware 'auth' and controller with middleware 'auth'.

Maybe framework/src/Illuminate/Routing/Route.php gatherMiddleware() must return only unique values ?

class MainController extends Controller
{

    public function __construct()
    {
        $this->middleware('auth');
    }
}


Route::group(['middleware' => ['auth']], function () {

    Route::get('/first', 'MainController@index');
}

Route::get('/second', 'MainController@index');

php artisan route:list

before:

| Domain | Method   | URI    | Name  | Action                                      | Middleware |

|        | GET|HEAD | first  |       | App\Http\Controllers\MainController@index   | web,auth,auth
|        | GET|HEAD | second |       | App\Http\Controllers\MainController@index   | web,auth

after fix:

| Domain | Method   | URI    | Name  | Action                                      | Middleware |

|        | GET|HEAD | first  |       | App\Http\Controllers\MainController@index   | web,auth
|        | GET|HEAD | second |       | App\Http\Controllers\MainController@index   | web,auth

Would it be more preferable if artisan route:list displayed middleware from route and controller separately?

For example:

| Domain | Method   | URI    | Name  | Action                                      | Middleware |

|        | GET|HEAD | first  |       | App\Http\Controllers\MainController@index   | [r]web,auth [c]auth
|        | GET|HEAD | second |       | App\Http\Controllers\MainController@index   | [r]web [c]auth

[actionm]

fixed branch to 5.3 from #16173