Removes an item from a treeview (either a leaf or a complete node). You have to pass
the id of the entry to remove in item$. Alternatively, you can also pass one of the
following special values in item$:
Active
Removes the active item.
Root
Removes all items in the treeview. This does the same as calling the
Treeview.Clear method. (V2.0)
Inputs
id
id of the treeview object
item$
id of the tree item to remove or special value (see above)