I don't think we can completely remove them, because doing so would conflict with an important part of the blurb in the election page's sidebar:
The candidate vote scores are all public.
Since all votes cast to nominations are public, they arguably have to remain accessible somehow even if a nomination is withdrawn further down the line.
However, position statements in withdrawn nominations are indeed unactionable and do make up the bulk of the post. I second you on that point, and would suggest we only hide the position statement but keep the candidate's user card and vote count visible, albeit dimmed in the usual way.
EDIT: Another candidate has chosen to delete his position statement himself before withdrawing, which achieves the same effect.