So you were experimenting, and turned on the feature called "Content Organizer", or maybe you tried it out and decided it wouldn’t work for your environment. But, unbelievably, even if you turn off the feature, you still can’t delete the library. That’s because Microsoft turned a property off for this library (probably with good reason, you can imagine an uninformed user deleting it with the feature turned on and causing all kinds of havoc). The property is called "AllowDeletion", and is not available to turn back on through the normal UI. PowerShell to the rescue!
$site = get-spweb http://site/web
$dropOffLibrary = $site.Lists["Drop Off Library"]
$dropOffLibrary.AllowDeletion = "True"
After running this, the delete this library option will magically reappear