Bug 1052136 - Clean up mozL10n API use in Communications, part 5, matching+utilities

https://bugzilla.mozilla.org/show_bug.cgi?id=1052136
there is a more terse way to do this

```js
var msidsn = sim.iccInfo && sim.iccInfo.msisdn;
var msg = msisdn ? 'simNumberWithMSISDN' : 'simNumber';
var msgParams = {
  number: index,
  msidsn: msisdn
}
navigator.mozL10n.setAttributes(msg, msgParams)
```