This commit contains a couple of improvements for this
rake task.
* We no longer limit the uploads to only ones with Post
upload references, it doesn't matter what the secure uploads
are linked to, they should all be un-secured
* We now only get distinct uploads from the initial query,
multiple upload references on the same upload caused
double ups and confusing counts for the task
* We now also disable the secure_uploads_pm_only site
setting at the same time