Fixing the colorization of legacy media notifications

Previously the colorization wouldn't work if the notification
was not targeting N and above, since for those the
remoteviews would be built into the notification and we couldn't
colorize it.

Test: runtest -x packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/MediaNotificationProcessorTest.java
Fixes: 38147364
Fixes: 37743600
Change-Id: Iabad02a4515c42676c0660293e58cf62d5d8ff88