Ticket 47732 - ds logs many "SLAPI_PLUGIN_BE_TXN_POST_DELETE_FN plugin returned error" messages
    
    Bug Description:  there are many error messages relate to postop delete plugins
    			whichare not justified
    
    Fix Description:   the usn plugin always returns an error when an attempt is made
    			to delete a non-existing entry, checking the ldap code in
    			the pblock.
    			But the plugin executes correctly and the error is aleady set
    			so return succes
    
    https://fedorahosted.org/389/ticket/47732
    
    Reviewed by: richm, thanks