Revert of New PeerConnectionInterface::GetStats: No bogus default implementation. (patchset #1 id:1 of https://codereview.webrtc.org/2566143002/ )

Reason for revert:
Breaks google3 importer:
http://webrtc-buildbot-master.mtv.corp.google.com:21000/builders/WebRTC%20google3%20Importer/builds/11260

Original issue's description:
> New PeerConnectionInterface::GetStats: No bogus default implementation.
>
> The Chromium mock implementation implements the new GetStats API, so we
> can remove this default implementation.
>
> BUG=chromium:627816
>
> Committed: https://crrev.com/8f2309478da41cd8b829d022874dfd5ddc58551c
> Cr-Commit-Position: refs/heads/master@{#15563}

TBR=deadbeef@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:627816

Review-Url: https://codereview.webrtc.org/2575493002
Cr-Original-Commit-Position: refs/heads/master@{#15567}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: e381015ca0c1104edfd0688bcedff29b2e4eae07
1 file changed