message_list_data: Replace lodash with standard Array methods.
message_list_data: Replace lodash with standard Array methods.

Array#findLastIndex is new in ES2023, but is polyfilled with core-js ≥
3.16 and supported in Node.js 18.

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulip.com>

zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip