Removes the item and its descendants from the outline and from the document.
public void Remove()
ISO 32000-2 §12.3.3, Tables 150 and 151. The item's neighbours are linked to each other, its parent's First,
Last and Count and its ancestors' Count entries are corrected, and the item and its descendants are removed
with RemoveObject(CosReference) (a save writes their numbers as free entries); an item the rest of the outline
still reaches through damaged links is kept. The view must not be edited afterwards.