Remove FXIOS-13960 [MozillaOnline] Do not set regional mode based on locale

[janbrasna]

:scroll: Tickets

Jira ticket FXIOS-13960 Github issue #30264

:bulb: Description

Stops flipping AppInfo.isChinaEdition based on just the app/device regional locale (while keeping other testing, debug & hidden prefs intact, full removal to be ticketed separately).

Desktop and Android stopped shipping their repacks similarly configured earlier this year.

The domestic infra is going away. FxA https://github.com/mozilla/application-services/pull/7060 will point it to prod anyways soon; this accompanies it by hiding the prefs that stop having any effect. Everyone will get just the same global experience.

(If that proves to be a viable change in behavior going forwards, all the supporting settings, screens, config, debug settings, and testing stack can be removed as a next step.)

:pencil: Checklist

• [x] I filled in the ticket numbers and a description of my work
• [x] I updated the PR name to follow our PR naming guidelines
• [ ] I ensured unit tests pass and wrote tests for new code
• [ ] If needed, I updated documentation and added comments to complex code

[github-actions[bot]]

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[ih-codes]

@adudenamedruby Looks like you took a first review on this, can you take another look to see if it's good? Thanks!