[#1471] Fix dataset deletion authorization for unowned datasets

We are basically deferring the whole package_delete auth function to
package_update, because deletions are basically changing the state field
of a dataset from 'active' to 'deleted'.
[#1471] Call proper function on package_delete
[#1471] Fix old test

Since organizations were implemented, any unowned dataset can be edited
(and thus deleted) by any user.
We will probably improve this in th future using the creator_user_id