Disable MediaNotificationProcessor

Disabling MediaNotificationProcessor when the new media experience is
enabled. The notification views that are inflated won't be shown anyway
so it is just a waste of time and memory.

Fixes: 157732475
Test: manual - heap_profile systemui while SoundCloud is playing. Verify
that flame graph doesn't show a hotspot for MediaNotificationProcessor.processNotification

Change-Id: I252697255ce2b30c99d244acd4e30cd56eb0416d