Remove user rights (task CE-729)

Removing global user rights + asynchronous task, which removes all user's rights from all Wikias.
I don't think this works the way you think it does - INSERT() has 2 parameters: table and columns. This usage suggests the second parameter is a hash of column name => column value pairs. This should be used as:

```php
$rowValues = [];
foreach ($groups as $group) {
  $rowValues[] = [$userId, $group];
}
(new \WikiaSQL())->INSERT('user_former_groups', ['ufg_user', 'ufg_group'])
->VALUES($rowValues);
```