Hide the default browser settings again after MozBug 1969949

🔍 Bugzilla Audit

Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1969949

Commit: 9d7faf03

Description

9d7faf03 refactored the default browser box, so I dropped our TB 41822: Unconditionally disable default browser UX in about:preferences patch.

We'll need to re-implement it.

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