Allow admins to remove votes on posts. This is for fixing vote abuse.
Votes can be removed by going to the vote list on the /post_votes page,
or by clicking on a post's score, then using the "Remove" option in the
"..." dropdown menu next to the vote.
Votes are soft-deleted - they're marked as deleted in the database, but
not fully deleted. Removed votes are only visible to admins, not to
regular users. When a vote is removed by an admin, it leaves a mod
action.
Technically it's possible to undelete votes, but there's no UI for it.
