Naming two variables the same way is confusing at the very least, and
can lead to hard to debug errors. That's why the Ruby interpreter issues
a warning when we do so.
The code `where(id: ids)` is equivalent to `where(id: ids.uniq)`.
Since Rails 5 uses `distinct` instead of `uniq` and in most cases where
we use `uniq` with `pluck` we should simply remove the `uniq` call (as
done in this commit), we're also removing the `Rails/UniqBeforePluck`
rubocop rule.
