Remove dependencies on Chromium's webrtc_overrides.
Remove dependencies on Chromium's webrtc_overrides.

In system_wrappers, two build targets depended on the Chromium's
//third_party/webrtc_overides folder. While this was acceptable
before, now that the WebRTC component build is landed [1] it can
create a path where parts of WebRTC get statically linked in
Chromium. To avoid this, this CL removes them and fixes the
problem in //third_party/webrtc_overides.

[1] - https://chromium-review.googlesource.com/c/chromium/src/+/1874722

Bug: webrtc:9419
Change-Id: I94c739d15eb974371af8087986cee03794f327dc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/159862
Reviewed-by: Karl Wiberg <2c708eb0a58047bf403399f50b3da33ffd2dd444@webrtc.org>
Commit-Queue: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#29852}

TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc