SDK / exoplayer

Really low hanging fruit optimization for TS extraction.

ParsableBitArray is quite expensive. In particular readBits
contains at least 2 if blocks and a for loop, and was being
called 5 times per 188 byte packet (4 times via readBit). A
separate change will follow that optimizes readBit, but for
this particular case there's no real value to using a
ParsableBitArray anyway; use of ParsableBitArray IMO only
really becomes useful when you need to parse a bitstream more
than 4 bytes long, or where parsing the bitstream requires
some control flow (if/for) to parse.

There are probably other places where we're using
ParsableBitArray over-zealously. I'll roll that into a
tracking bug for looking in more detail at all extractors.

Issue: #3040

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=161650940