We were checking for `expired?` and `results_enabled?` in views and
helpers, when we've already defined a rule for accessing stats and
results for a poll.
This way we also fix a bug when stats were enabled but the poll wasn't
finished. In this scenario, the link pointed to the stats page, but when
clicking it we'd get a "you don't have permission" message.
Now the link doesn't point to the stats page anymore.