Removing tags is not working in Google Reader API

There is an improper comparison when checking the tag name when removing tags on line: https://github.com/FreshRSS/FreshRSS/blob/master/p/api/greader.php#L350

```php
if ($remove != '' && strpos($remove, 'user/-/label/'))
```

Should be:
```php
if ($remove != '' && strpos($remove, 'user/-/label/') === 0)
```
