Enhancement: worf-delete-subtree to update the todo count

[heikkil]

I found a solution to this emacs stackexchange question and then started to think that it could a good addition to worf-delete-subtree.

I am not too sure about the design philosophy behind worf and implications of adding this functionality, so rather than creating a pull request, I suggest here that this could be added to the end of the worf-delete-subtree function code:

(when org-provide-todo-statistics
      (org-update-parent-todo-statistics))

At least, there is very little overhead in adding it. At best, updating the stats automatically could be a pleasant surprise to the user. There might be other places where org todo stats could be taken into account, but not sure where.