[Developers] Deleting /book/book_editor

[Bryan Cheung]

https://bugs.freebase.com/browse/DA-555

This type was supposed to be deleted during an earlier refactoring,  
but was missed.  If there are still applications still using this  
type, they should be updated to query the /book/author/works_edited  
property.  I'm planning on deleting this type on 1/19/2009; if there  
is any problem with this or if anyone needs more time for query  
updates, please speak up.

Bryan