chore: remove backstopjs from dependencies.

[worldomonation]

Related to #73601.

Proposed Changes

This PR removes backstopjs, workarounds, scripts and files associated with the visual regression tests.

Context: p1677001849898539/1676996972.514049-slack-C02DQP0FP

Key changes:

• remove entire directory under test/visual.
• remove dependency on backstopjs which in turn removes its dependency on puppeteer:5.5.0, which was causing errors on Apple Silicon.
• remove scripts associated with visual regression.
• update documents where required.

Testing Instructions

Ensure the following build configurations are passing:

• Unit Tests
• Any E2E test
• Code Style
• Docker image

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-58190

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-58190&env=jetpack

[karenroldan]

LGTM 🚀 I've also triggered the pre-release tests and all tests passed.

praise: the updates on the docs are also appreciated! 👍🏻

[jsnajdr]

Hi @worldomonation 👋 Since this PR was merged to trunk, the "Calculate ICFY stats" GitHub action is not running and not submitting stats to iscalypsofastyet.com. That's because the PR removes the PUPPETEER_SKIP_DOWNLOAD env variable from icfy-stats.yml, but leaves the now-empty env: key, which is probably some kind of YAML syntax error.

Fixing this in #73808.