Fix indentation for stub object classes

This removes the extra indentation before `class` or `abstract class` in generated stub object classes.

Before:
```php
<?php

namespace Propel\Tests\Bookstore;

use Propel\Tests\Bookstore\Base\Author as BaseAuthor;

        class Author extends BaseAuthor {

}
```

After:
```php
<?php

namespace Propel\Tests\Bookstore;

use Propel\Tests\Bookstore\Base\Author as BaseAuthor;

class Author extends BaseAuthor {

}
```