Bulk Domain Transfer: Redirect from start to stepper

[escapemanuele]

Context

MERGE ONLY WHEN STEPPER BULK DOMAIN TRANSFER FLOW IS COMPLETED.

• This PR redirects from /start/domain-transfer to /setup/domain-transfer, hence using the new domain-transfer flow built using Stepper
• Removes the flow flag

Testing

1. Live Link
2. Visit /start/domain-transfer, you should land in /setup/domain-transfer

Fixes https://github.com/Automattic/dotcom-forge/issues/2926

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-72623

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-72623&env=jetpack

[matticbot]

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

App Entrypoints (~20 bytes removed 📉 [gzipped])

name           parsed_size           gzip_size
entry-stepper        -61 B  (-0.0%)      -20 B  (-0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

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.

[alshakero]

Perfect.

[ebinnion]

I've already updated the buttons in the landing pages and there are existing issues in /start/domain-transfer, so I'm going to deploy this.