I think,, if Wolpi just hope to remove reference to “UNASSIGNED” in category,
(so that,, saved scene etc show in as “UNASSIGNED”)
on this case,, you may need not use content DB maintenance,, etc.
it can reomve orphan files, but, unassgined files are not orphan files.
open content library
Categories>Default>Unassigend> your files.
simply Right click the file ( image) or directory of category.
then select ” remove referrence.” (file) or “delete” (directory)
it remove only the refference to UNASSGINED”
after that, you may need “reflesh” (right -click on database icon (catgory) in content library)
some times to remove icon. but it work.
though you can not remove “Unussigend ” category from content library, I think.
you can delete only files reference and sub directory from Unassigned.
but in smart content, “Unassigend ” has gone out 
so you may keep safety your secret scene,,may be,,,
however if you save new secret scene, and you do not categorize it,,
it must be shown in unassgined category in smart content view ^^;
so you may need often delete directory from category unussigned,,
Seriously spend sometime clicking everything you can find, open this that and the other. I do this for at least a week with a new piece of software before I go searching for tutorials. Then I am able to follow the help a little easier with having familiarised myself with the User Interface. There is always a Cancel button. 
