Switch "UTC time" to "Unix epoch time"

This is more correct. Android devices, even under ideal conditions,
don't track UTC (which contains leap seconds and uses the SI definition
of a second) but use a clock based on Unix epoch time (no leap seconds,
but clocks may skip/stop or smear around leap seconds to ensure a fixed
number of second increments per calendar day when leap seconds are
applied to UTC).

Bug: 218802673
Test: Compile only
Change-Id: I4c5435bdb3bb124d4cb465a966bd43d58b640421

res/values/strings.xml

@@ -597,7 +597,7 @@
     <string name="date_and_time_settings_title_setup_wizard">Set date and time</string>
     <!-- Main Settings screen setting option summary text for the item to go into the date and time settings. -->
     <string name="date_and_time_settings_summary">Set date, time, time zone, &amp; formats</string>
-    <!-- Date & time setting screen setting switch title: whether the system clock (UTC time) should be determined automatically [CHAR LIMIT=100] -->
+    <!-- Date & time setting screen setting switch title: whether the system clock (Unix epoch time) should be determined automatically [CHAR LIMIT=100] -->
     <string name="date_time_auto">Set time automatically</string>
     <!-- Date & time setting screen setting switch title: whether the time zone should be determined automatically [CHAR LIMIT=100]  -->
     <string name="zone_auto_title">Set time zone automatically</string>