Fix phantom subscriptions

From #640508-9: Lock sources before importing/expiring/clearing them:

Got duplicates with feeds_nid 0. This was due changing the feed from manual (stand-alone-form) to being attached to a content type.

Though in the feeds_sources the reference did not get deleted to the stand-alone-form. And so content got imported twice. I manually deleted the row from feeds_sources

We should fix this with the next release.