Remove CPU architecture type detection from site.js

[alexgibson]

Description

I need to double check first, but I think since #14096 was completed we no longer need to keep the archType UA checks that are still in site.js.

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Success Criteria

• Verify that there's nothing left that relies on detecting CPU type (e.g. ARM).
• Remove archType functions and code from site.js.

[janbrasna]

There's an open issue for Chromebooks: #8006 that refers (=is caused by?) this sniffing. Can't tell if removal of the arch detection makes the Chromebook results better or worse, just wanted to mention it.

[alexgibson]

@janbrasna if removing this code helps fix one of those false positives then it's another reason to simplify 👍

[janbrasna]

Additionally I think the .arm body class added to the /thanks page has no effect today — it used to show a link to sumo, but that's long gone, and today even the linux-arm explainer is removed in favour of generic instructions. Windows ARM64 detection is removed too #9768, so this seems OK.

The ARMv8-A are still tested via getArchSize("aarch64") if needed so this all looks like just an old, unused code. 🚢