loops: Rewrite false `reduce` with `forEach`, in aggregateReactions.
loops: Rewrite false `reduce` with `forEach`, in aggregateReactions.

As in previous commits, this is a maximally boring and mechanical
rewrite.

The diff can look misleadingly big because the indentation changed.
To read it, try ignoring whitespace, e.g. with `git log -p -b`.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile