SDK / exoplayer

Both of these features are being promoted to first class
citizens in V2 (multi-period support will be handled via
playlists, seeking-in-window will be handled by exposing
the window/timeline from the player and via the normal
seek API). For now, it's much easier to continue the
refactoring process with the features removed.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=119518675