Remove the admin_style_v3 toggle from Production and Staging environments

[chahmedejaz]

What? Why?

• Closes Remove the admin_style_v3 toggle from production and staging environments #12911
• This PR removes the admin_style_v3 feature toggle for staging and production envs
• Moreover, it ensures that you can see the toggle in development env.

What should we test?

• As described in the issue

Release notes

Changelog Category (reviewers may add a label for the release notes):

• User facing changes
• API changes (V0, V1, DFC or Webhook)
• Technical changes only
• Feature toggled

[chahmedejaz]

We can remove old bulk update specs now as we won't be using it anymore.

[dacook]

I was wondering if this would be straightforward or not..
I guess not! Thanks for working this out.

It's a bit complicated, but hopefully we can remove it again soon anyway.

[rioug]

@chahmedejaz can you fix the conflict ?

[chahmedejaz]

Thanks @dacook and @rioug - Conflicts have been resolved.

[mkllnk]

Good quick solution. I hope that we can remove the old code completely soon.

[drummer83]

Looking good! Merging! Testing notes will follow...

[drummer83]

Hi @chahmedejaz,
Thanks for working on this. Here are my testing notes now.

Before staging

• Feature toggle before staging:
  

• Page products_old can be loaded:
  

After staging

• Feature toggle after staging:
  

• Page product_old cannot be loaded anymore.

• I couldn't find any broken links linking to the product_old page.

• I did not test anything regarding the toggle in the development environment, because I think it's not critical.

Thanks again! 🙏