unread: Avoid use of opaque message.
unread: Avoid use of opaque message.

We only care about ~8 fields from a Zulip message
when we're tracking unread counts. For example, we
don't care about the "content" field. This also sets
us up to pull up the "display_recipient" logic in an
upcoming commit.

zulip/zulip,andersk/zulip,andersk/zulip,kou/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,zulip/zulip,rht/zulip,zulip/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,andersk/zulip,rht/zulip,rht/zulip,rht/zulip,kou/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,kou/zulip,zulip/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,eeshangarg/zulip,eeshangarg/zulip,andersk/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip