Revert behavior of DateUtils.formatElapsedTime

Change Ib3c1e1aad05827df646aa18645cce19dffb7551f fixes the inability
to display more that 2-digit hour values, but also changes the behavior
of <10 minutes display by zero-padding the minutes. This makes
the Chronometer widget look different, and breaks Holo CTS.

Fix it so that for values under 600 seconds, the minutes don't
get padded

Change-Id: Iee043b698135bd4aedccf8f1a33f7b9493f960ae