Issue 6485 - Fix double free in USN cleanup task

Description:

ASAN report shows double free of bind dn in the USN cleanup task data. The bind
dn was passed as a reference so it should never have to be freed by the cleanup
task.

Relates: #6485

Reviewed by: ?

ldap/servers/plugins/usn/usn_cleanup.c

@@ -362,8 +362,6 @@ usn_cleanup_task_destructor(Slapi_Task *task)
         if (mydata) {
             slapi_ch_free_string(&mydata->suffix);
             slapi_ch_free_string(&mydata->maxusn_to_delete);
-            slapi_ch_free_string(&mydata->bind_dn);
-            /* Need to cast to avoid a compiler warning */
             slapi_ch_free((void **)&mydata);
         }
     }