api_docs: Clean uses of shared emoji schemas in OpenAPI.
api_docs: Clean uses of shared emoji schemas in OpenAPI.

Reformats two events (`reaction op: add` and `reaction op:remove`)
to follow the general format of events in the OpenAPI that are
returned by the `/get-events` endpoint.

Removes unneeded reference to `EmojiBase` schema in `user_status`
return value for the `/register-queue` endpoint. Also, clarifies
the text about the `user_status` object and fields being returned.

zulip/zulip,andersk/zulip,andersk/zulip,andersk/zulip,zulip/zulip,rht/zulip,rht/zulip,rht/zulip,andersk/zulip,rht/zulip,andersk/zulip,zulip/zulip,zulip/zulip,andersk/zulip,andersk/zulip,rht/zulip,rht/zulip,zulip/zulip,rht/zulip,zulip/zulip,zulip/zulip