Revert of Fix chromium-style warnings. (patchset #1 id:1 of https://codereview.webrtc.org/2400993002/ )

Reason for revert:
Broke internal project

Original issue's description:
> Fix chromium-style warnings.
>
> Separate the null implementation from rtp_rtcp_defines.h, and follow chromium style guide for virtual functions.
>
> BUG=webrtc:163
>
> Committed: https://crrev.com/509eadd554de6bf938da08071c5d2c2541703134
> Cr-Commit-Position: refs/heads/master@{#14738}

TBR=danilchap@webrtc.org,kjellander@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:163

Review-Url: https://codereview.webrtc.org/2449523002
Cr-Original-Commit-Position: refs/heads/master@{#14750}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 838cdb3db6a24b9be3a3d2700144197935415463
11 files changed