Bug 1040271 - [L10n][SMS] Clean up mozL10n.get uses in SMS app

Far simpler is to have:
```
info = [operator, number].filter(function(value){
    return value;
  });

var detail-string = info.join(',');

if (simId){
    l10nId = info.length ? 'sim-id-label' : 'sim-detail';
    data = {sim: simId, detail-string: detail-string};
    navigator.mozL10n.setAttributes(
        element.querySelector('.sim-detail'),
        l10nId,
        data);
} else {
    element.querySelector('.sim-detail').textContent = detail-string;
}
```

with locale
```
sim-id-label = SIM {{sim}}
sim-detail = SIM {{sim}}, {{detail-string}}
```