Bug 1043615 - Clean up mozL10n.get uses in Settings app

https://bugzilla.mozilla.org/show_bug.cgi?id=1043615
Yeah, that's what I would consider more error-proof:

systemStatus.setAttribute('data-l10n-id', l10nVaues.indexOf(value) !== -1 ? value : 'check-error');

But I'm not sure where to take l10nValues list from.