'Remove the sticky (top) comment for this link, if it exists.
`comment` is an optional argument that, if set, will ensure the
sticky comment matches. If it does not match, it will not remove. If
`comment` is unset, it will remove regardless of ID.
`set_by` is an optional Account, which if set will add a ModAction
event to the mod log.'

def remove_sticky_comment(self, comment=None, set_by=None):

    if (self.sticky_comment_id is None):
        return
    if (comment and (self.sticky_comment_id != comment._id)):
        return
    prev_sticky_comment = Comment._byID(self.sticky_comment_id)
    self.sticky_comment_id = None
    self._commit()
    if set_by:
        ModAction.create(self.subreddit_slow, set_by, action='unsticky', target=prev_sticky_comment)
