These tests don't use the browser to send emails since commit e21588ec1.
However, note that this commit actually actually decreased our test
coverage somehow; since then, we're no longer testing whether we send an
email to the author after clicking the "Publish comment" button. We
might need to add a test for this in the `spec/system/comments_spec.rb`
file... but that's a story for another time.
Note we need to stub the `deliver_later` method; otherwise,
`open_last_email` would raise an exception since no email would have
been delivered.
We're moving them now because these tests use the `open_last_email`
method, and we're looking for places where using this method might
result in a flaky test when used inside a system test.
We take the comment as a parameter instead of the user, since usually
people reply to comments and not to users.
We also remove one database query after the browser has started, since
we can use `debate_path(debate)`. It's also more clear why we're using
`debate_path` in the test; before these changes, we had to enter the
`reply_to` method to realize that we were replying on a debate.
