Minor copybara fixes
Minor copybara fixes

- Remove proguard-rules.txt symlink
- Guard against classes annotated with @ClosedSource but not excluded

PiperOrigin-RevId: 311312671

google/ExoPlayer,stari4ek/ExoPlayer,amzn/exoplayer-amazon-port,ened/ExoPlayer,androidx/media,stari4ek/ExoPlayer,ened/ExoPlayer,amzn/exoplayer-amazon-port,androidx/media,ened/ExoPlayer,androidx/media,google/ExoPlayer,amzn/exoplayer-amazon-port,stari4ek/ExoPlayer,google/ExoPlayer