DeskClock: Hide or disable some screensaver settings

* Based on the current choices, some settings don't make sense to display
  at all:
  * Analog design: Neither bold clock text nor AM/PM indicator are
    relevant at all
  * Locale with 24h format: AM/PM doesn't make sense to offer

Change-Id: Icd66a4bfeb349913b536f0a5de5dc1e415224473