Update DeskClock to use v4 NotificationCompat

v7 NotificationCompat's DecoratedCustomViewStyle
has been deprecated and folded into the v4
NotificationCompat. By updating the imports, we
avoid using the deprecated versions and fully
switch to the new versions.

Test: mmma packages/apps/DeskClock
BUG: 28983951
Change-Id: I9028f3f048fc3857a24fa83f5ed075107d85e7cf