Revert "Make WebRTC-RTP-Lifetime enabled-by-default."

This reverts commit 0deb9d6d33111cbf2a5b248434870dd9d8b982fc.

Reason for revert: Breaks internal test that assumes RTP stats exist
prior to reception

Bug: chromium:406585888
Original change's description:
> Make WebRTC-RTP-Lifetime enabled-by-default.
>
> Ships spec-compliant RTP stats lifetimes as per Intent to Ship:
> https://groups.google.com/a/chromium.org/g/blink-dev/c/GYqPzIUUZCQ
>
> The TL;DR change is:
> 1. outbound-rtp creation is delayed until O/A has completed, but can
>    exist prior to sending any packets.
> 2. inbound-rtp creation is delayed until first packet has been received,
>    whether or not O/A has completed (allowing early media use case).
>
> The flag is kept as a kill-switch, to be removed after this has reached
> Chrome stable.
>
> Bug: chromium:406585888
> Change-Id: Ibb42d77eb156ba14d2f50e6521d51615551fe489
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/406620
> Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> Commit-Queue: Henrik Boström <hbos@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#45468}

Bug: chromium:406585888
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I0dad2172691d78945b82a7796e51a42cace85d33
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/406761
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Henrik Boström <hbos@webrtc.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#45470}