Revert of Simplify and extend RtpHeaderExtensionMap (patchset #12 id:260001 of https://codereview.webrtc.org/2452293004/ )

Reason for revert:
breaks downstream project

Original issue's description:
> Simplify and extend RtpHeaderExtensionMap
> Add register functions for various codepaths.
> Add initialize-list constructor to create usable const RtpHeaderExtensionMap
> Optimize implementation for GetId/GetType.
>
> BUG=webrtc:1994
>
> Committed: https://crrev.com/d1d26fbeb37a69471a34004c6ac2d3fafde5d404
> Cr-Commit-Position: refs/heads/master@{#14986}

TBR=sprang@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:1994

Review-Url: https://codereview.webrtc.org/2484863007
Cr-Commit-Position: refs/heads/master@{#14988}