Change getAgeMillis to use elapsed system time instead of wall-clock time.

Changing getAgeMillis to rely on SystemClock#elapsedRealtime() to determine
the duration of a call.  This ensures that changes to the device time zone,
clock updates by the network and user initiated time changes to not
impact the duration of calls in the call log.

Test: Manual, unit
Bug: 64068300
Merged-In: I62924dc7889c86a7457d05f8fbb20ab8189ece1a
Change-Id: I62924dc7889c86a7457d05f8fbb20ab8189ece1a
(cherry picked from commit 6c3a2dd6)