uBlock enables and downloads per-region/language additional blocklists

Reported by wb:2198b57911ce2246ba27e649caac5109, reproduced in 5.19: if I choose French locales in the Welcome Screen, when I start Tor Browser, uBlock enables and downloads the "AdGuard Français" lists.

We're told that some fingerprinting sites (like https://browserleaks.com/proxy) can detect this new filter and this is a regression in recent uBlock. I did not confirm any of that.

These filters, defined in assets.json, are enabled like that:

        if (
            assetEntry.content === 'filters' &&
            assetEntry.external !== true
        ) {
            assetEntry.isDefault =
                assetEntry.off === undefined ||
                assetEntry.off === true &&
                    µb.listMatchesEnvironment(assetEntry);
        }

We could patch that code, or patch µb.listMatchesEnvironment to always return false, or programmatically remove per region/language filters ("group": "regions") from assets.json. This last option has greater chances to keep working across upgrades (no fuzzy patches that fail to apply), so I like it; but to avoid it silently stopping working we should ensure we are indeed removing some/enough filters.

Tentatively adding this to the FT short-term plate because it looks like a pretty bad fingerprinting bug (assuming we don't already leak the locale in other ways) with simple & cheap solutions.