Revert "AudioEncoderDecoderIsac: Merge the two config structs"

Reason for revert - breaks Hangouts

This reverts commit 7c324cac50ac38122b3f3b26455bc55ad834bfc0.

BUG=chromium:478161

Review URL: https://webrtc-codereview.appspot.com/43209004

Cr-Commit-Position: refs/heads/master@{#9030}
4 files changed