Revert of Opus implementation of the AudioDecoderFactoryTemplate API (patchset #1 id:1 of https://codereview.webrtc.org/2942733003/ )

Reason for revert:
breaking downstream projects

Original issue's description:
> Opus implementation of the AudioDecoderFactoryTemplate API
>
> BUG=webrtc:7837
>
> Review-Url: https://codereview.webrtc.org/2942733003
> Cr-Commit-Position: refs/heads/master@{#18646}
> Committed: https://chromium.googlesource.com/external/webrtc/+/d053fe4ab36a77db866fb813fec825a116590704

TBR=ossu@webrtc.org,solenberg@webrtc.org,kwiberg@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:7837

Review-Url: https://codereview.webrtc.org/2944763002
Cr-Original-Commit-Position: refs/heads/master@{#18648}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: eb2d2d31d17e92fba4621d9af3baeca13dd51e0c
11 files changed