Switch to AppRTC provided by webrtc/src.

This uses the simpler extraction script and packaging method developed in https://webrtc.googlesource.com/src/+/1d7392a45c95794b385f6a7c3a9dfa5428c4bbed

https://chromium-review.googlesource.com/c/chromium/src/+/992320 updates the paths

Bug: webrtc:7602

Change-Id: Ia10eb621a8903e2193621a624de14958d22a06ad
Reviewed-on: https://webrtc-review.googlesource.com/66463
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>