Don't show badge for media style notifications

Fixes: 156834522
Test: manual - Play audio with Castbox. Verify that a badge does not
appear on the app icon.
Test: atest uiservicestests/src/com/android/server/notification/BadgeExtractorTest.java
Test: atest uiservicestests/src/com/android/server/notification/PreferencesHelperTest.java

Change-Id: Ie1ade943215c0b7895956d65064c310d555c6c88