Clean up release notes for 2.12: UI, downloads, DRM
Clean up release notes for 2.12: UI, downloads, DRM

PiperOrigin-RevId: 326427225

amzn/exoplayer-amazon-port,androidx/media,androidx/media,google/ExoPlayer,ened/ExoPlayer,amzn/exoplayer-amazon-port,ened/ExoPlayer,amzn/exoplayer-amazon-port,google/ExoPlayer,androidx/media,ened/ExoPlayer,google/ExoPlayer