Bug 1027313 - [B2G][Contacts][Facebook]Removing all Facebook Data from d...

...evice without other Contacts saved displays Delete Contacts button to select contacts that do not exist
I think a more logical structure for the tests could be:

```js
document.addEventListener('fb_cleaned', function cleaned() {
  navigator.mozContacts.number = 0;
})
 document.dispatchEvent(new CustomEvent('fb_cleaned'));
 var bulkDelContacts = document.getElementById('bulkDelete');
 assert.equal(bulkDelContacts.getAttribute('disabled'), 'disabled');
```