See comment, but TLDR this is for backwards-compatibility.
(See 479628, where it failed to dismiss after fixing.)
We don't bother with `prepare.js` because it always errors
(and so should never be dismissed).
I have simply added the needed comments to each of `check-target-branch.js`'s
pre-existing reviews, because there are so few.
Dismissals are done automatically by commits.js, even for reviews from
check-target-branches.js. This is not desirable.
The solution is
(1) do not decline to post a review because it was already dismissed
(because it may have not been dismissed by a human, and circumstances may
have changed), and
(2) reword the auto-dismissal message to not imply that whatever
problems were present are fixed.
When a user deletes their account, they appear as a "ghost user". This
user is represented as `null` on API requests. If such a user had posted
a review before, this breaks a few places, which assume to be able to
access `user.login`.
