Disallow vp8 MediaCodec in MediaCodecUtil instead of AVDA.

Needs to be done in MediaCodecUtil otherwise the EME types won't
incorrectly reject encrypted vp8 support.

BUG=612909
TEST=none

Review-Url: https://codereview.chromium.org/2348683002
Cr-Commit-Position: refs/heads/master@{#419045}
2 files changed