Reason for revert:
Did break the bots.
https://build.chromium.org/p/client.webrtc/builders/iOS32%20Release/builds/9807
Original issue's description:
> GN: Refactor modules_unittests to eliminate package boundary violations.
>
> Also move bwe_simulator to webrtc/modules/remote_bitrate_estimator
>
> BUG=webrtc:6954
> NOTRY=True
>
> Review-Url: https://codereview.webrtc.org/2649563002
> Cr-Commit-Position: refs/heads/master@{#16270}
> Committed: 36cb55d715
TBR=kjellander@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:6954
Review-Url: https://codereview.webrtc.org/2651023005
Cr-Commit-Position: refs/heads/master@{#16271}