Called after a given range is deleted from the editor (and after the display is refreshed; use on-delete and begin-edit-sequence to avoid extra refreshes when after-delete modifies the editor).
See also can-delete? and on-edit-sequence.
No internals locks are set when this method is called.
The start argument specifies the starting position of the deleted range. The len argument specifies number of deleted items (so start + length is the endig position of the deleted range).