Fix UI flicker problem and update wordings

- "Set time zone automatically" changes to "Set automatically".
- "Use location to set time zone" changes to "Use location"
- Add a new summary text with "Location may be used to set time zone".

Fixes: 233968737
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.datetime
Change-Id: Ia16c428e906cda4ebe052bad83c3f574075a7a64

res/xml/date_time_prefs.xml

@@ -45,7 +45,6 @@
         <com.android.settingslib.RestrictedSwitchPreference
             android:key="auto_zone"
             android:title="@string/zone_auto_title"
-            settings:allowDividerAbove="true"
             settings:userRestriction="no_config_date_time"/>
 
         <!-- This preference gets removed if location-based time zone detection is not supported -->