Revert "Pull GN via CIPD package."
Revert "Pull GN via CIPD package."

This reverts commit 77cc8182aef6ec97ecd4c115fae5de4f511efa57.

Reason for revert: Breaks DEPS Auto-roller.

Original change's description:
> Pull GN via CIPD package.
> 
> The gn binary will be downloaded into third_party/gn.
> 
> The part about gn_win will be true only after the buildtools_revision
> will be updated by the Chromium roll.
> 
> This CL has been copied from https://chromium-review.googlesource.com/c/chromium/src/+/1117264/9/DEPS.
> 
> Bug: None
> Change-Id: I3fee1d9f6c39e508871798eeeb60d74ab7bc41d1
> Reviewed-on: https://webrtc-review.googlesource.com/86123
> Commit-Queue: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
> Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#23765}

TBR=d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org,oprypin@webrtc.org

Change-Id: I660196e48a626e87ec5ed722b2a169620494d74c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: None
Reviewed-on: https://webrtc-review.googlesource.com/86220
Reviewed-by: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
Commit-Queue: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#23778}
TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc