Stop setting fixed 12-hour and 24-hour time formats in layouts

For quite some time, these time formats have been chosen dynamically
by ICU using the current Locale. They are fetched via
android.text.format.DateFormat.getBestDateTimePattern(...)

These static formats set in layout code are at best irrelevant and at
worst red herrings.

Change-Id: If29dd3d87307bb1a01deff5f48e99a51c1d93a95