Newsletter flow: remove intro

[simison]

We rely on wordpress.com/newsletter as intro instead.

Remove intro step entirely. Alternative to #82984

The support page and other places where we link to intro are enough context/intro, and we want them onto action asap instead of asking again to start. Slack convo (p1697035720638429-slack-C02NQ4HMJKV).

Proposed Changes

• Remove intro step from newsletter flow, and logic managing conditionally showing it if we came from the marketing page.

Testing Instructions

• Test urls like
  /setup/newsletter?ref=newsletter-lp
  /setup/newsletter?ref=support-site-inline
  /setup/newsletter/intro?ref=newsletter-lp
  /setup/newsletter/intro?ref=support-site-inline
• Test logged out, and logged in
• Test that you see "signup start" event and normal "step start" events

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-ajp-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-84162

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-84162&env=jetpack

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~247 bytes removed 📉 [gzipped])

name             parsed_size           gzip_size
newsletter-flow       -662 B  (-4.3%)     -139 B  (-3.3%)
sensei-flow           -242 B  (-0.1%)     -108 B  (-0.1%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[simison]

I saw signup form appear twice in this flow when going through /setup/newsletter as unlogged. Needs investigation.