Fix todo-mode commands to move items and categories (bug#64298)

Fix todo-mode commands to move items and categories (bug#64298)

* lisp/calendar/todo-mode.el (todo-move-category): Restore display
of selected category in source file, so internal file structure is
not visible if user is prompted to choose a new category name in
target file, and widen again to delete moved category from source
file.
(todo-move-item): Don't use todo-forward-item when moving done
items, to avoid mislocation if done items sections of the the
target category was empty before moving.
(todo-forward-item): Remove commented out code meant to have the
effect of the above change in todo-move-item, but it did not work.