Fix error when not allowed to retract an item
Fix error when not allowed to retract an item

XEP-0060 §7.2.3.1 [1] states that "If the requesting entity does not have
sufficient privileges to delete the item, the service MUST return a <forbidden/>
error".

Fixes test "Retracting a local item should not be possible for anyone else".

[1]: http://xmpp.org/extensions/xep-0060.html#publisher-delete-error-forbidden

buddycloud/deprecated-buddycloud-server,buddycloud/deprecated-buddycloud-server