chore: Keep ip only within properties

[tiina303]

Problem

Trying to clean up our types. See also PostHog/plugin-scaffold#56
We don't need ip to be separate and it just creates confusion.
This is safe because the only apps that (should be) using ip are geoIP and advanced geoIP, both of which check both event.ip and event.properties.$ip
https://github.com/PostHog/posthog-plugin-geoip/blob/main/index.ts#L42 & https://github.com/paolodamico/posthog-app-advanced-geoip/blob/91b845841859fe8ec5a6f27c07df4ee3b43b0bde/index.ts#L87 respectively

Changes

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

How did you test this code?

There are already existing tests e.g.

posthog/plugin-server/tests/main/process-event.test.ts

Line 908 in ecd4771

test('ip override', async () => {

[bretthoerner]

Nice, good idea.

[bretthoerner]

Tests failed but it seems unrelated, I kicked the job.

[tiina303]

Tests failed but it seems unrelated, I kicked the job.

we run 4 different replicas of the functional tests - unless one touched anything that could break there as long as one of them passes we should be all good :)