Switch Chronometer to use ICU instead of duration_hours etc

The data in ICU has higher quality and is more comprehensive.
(Additionally, the old code was using spaces to separate hours,
minutes, and seconds, which was not correct for some locales.)

Finally, remove duration_hours etc, since there is no longer any user
of it.

Bug: 33670388
Bug: 19418509
Test: manual and CTS (cts-tradefed run cts-dev --module CtsWidgetTestCases --test android.widget.cts.ChronometerTest)
Change-Id: I97efa62186b94ed444fff90fa26bf71ac1599261