Bug 1035762 - [B2G][SMS] support 24 hour time format. r=schung

In not-download case, we still have 'expiry-date-format'  as l10nDateFormat dataset even it didn't have 12/24 dateFormat, so localization will still execute but actually there's no need to do so.  But maybe it's not really important because it only happens on not-download case?