SDK / exoplayer

1. The offloadSchedulingEnabled value doesn't need to be in
   PlaybackInfo because it's never updated in EPII.
2. The sleepingForOffload value in EPII wasn't updated explicitly
   (just via the return value of a method). It was also only
   meant to be enabled while the player is actively playing, but
   confusingly triggered from a path where the player may
   theoretically be buffering as well.
3. The offload sleeping (=not scheduling doSomeWork) was interwoven
   into the actual scheduling code making it slightly hard to follow.
   This can be improved slightly by keeping the offload sleeping
   decision and the scheduling separate.

PiperOrigin-RevId: 457427293
(cherry picked from commit aedde2de)