Simplify internal demo app
Simplify internal demo app

- Enable cleartext by default for the internal demo app
- Remove "external" variant of the internal demo app

PiperOrigin-RevId: 322987978

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