SDK / exoplayer

This list was meant to simplify some usages where we only want to
make operations on enabled renderers. However, keeping this list
up-to-date is slightly error-prone (because renderers aren't added
and removed from this list next to the corresponding enable and disable
calls) and it makes it hard to do more fine-grained changes that only
enable or disabled a single renderer at a time.

PiperOrigin-RevId: 300513788