Do not retain album art in NotificationMediaManager if unused

Album artwork is only needed here for lockscreen wallpaper, which is no longer
used by default.

- Update CentralSurfces SHOW_LOCKSCREEN_MEDIA_ARTWORK to be accurate
- If device does not use media lockscreen artwork: instead of saving the
  metadata as is, save a copy without artwork info, so we don't retain
  potentially large bitmaps in memory.

Bug: 278115559
Test: compare hprof - NotificationMediaManager memory reduced significantly
Test: atest NotificationMediaManagerTest
Test: manual - normal usage of media player unchanged
Change-Id: I2e203f581ad594a60bc3eec6f0782215c55b2ea5