g722 and red encoders: Use rtc::Buffer instead of scoped_ptr<uint8_t[]>

It's a win for red, and a toss-up for g722 since it never resizes its
buffer.

R=henrik.lundin@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/45219005

Cr-Commit-Position: refs/heads/master@{#9067}
4 files changed