Fix todo-mode bug involving archived items (bug#23447)

Fix todo-mode bug involving archived items (bug#23447)

* lisp/calendar/todo-mode.el (todo-jump-to-category): When jumping
from Todo Categories mode to a category with only archived items
and todo-skip-archived-categories is non-nil, make sure the
archive file buffer is in Todo Archive mode to prevent
todo-category-select from raising an error, and don't set
todo-current-todo-file, since that makes todo-show display the
archived category.  Remove a no-op call to kill-buffer, which is
already called in todo-insert-category-line.