Piecemeal conversion to draft needs to allow

already converted children.
STUD-1965

@cahrens please review (feel free to merge while I'm gone if it's ok)
Actually, I just care that the delete_item didn't raise an exception but I thought leaving it there w/o an assert seemed odd. I think I intended to look for the published of private_leaf since deleting the leaf shouldn't affect the published version of it. We could change this to whatever.