Revert r8342 "Switch to using AudioEncoderIsac instead of ACMISAC"

BUG=chromium:458638
TBR=kwiberg@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/33349004

Cr-Original-Commit-Position: refs/heads/master@{#8372}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 4dc0003bed431b573614b9f9e57956790132fb2f
4 files changed