Revert of Adding "first packet received" notification to PeerConnectionObserver. (patchset #4 id:60001 of https://codereview.webrtc.org/1581693006/ )

Reason for revert:
Seems that the end-to-end unit tests are now flaky: https://build.chromium.org/p/client.webrtc/builders/Win64%20Debug/builds/6283

Will reland after fixing the test flakiness.

Original issue's description:
> Adding "first packet received" notification to PeerConnectionObserver.
>
> R=glaznev@webrtc.org, pthatcher@webrtc.org, tkchin@webrtc.org
>
> Committed: https://crrev.com/42265a8cc3b3f3db4aa2c29005aed2fb4393adef
> Cr-Commit-Position: refs/heads/master@{#11401}

TBR=pthatcher@webrtc.org,tkchin@webrtc.org,glaznev@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.webrtc.org/1640173004

Cr-Commit-Position: refs/heads/master@{#11402}
15 files changed
tree: 0e74fc8f244369e9282f6273769651d02d378f33
  1. build_overrides/
  2. chromium/
  3. data/
  4. infra/
  5. resources/
  6. talk/
  7. third_party/
  8. tools/
  9. webrtc/
  10. .clang-format
  11. .gitignore
  12. .gn
  13. all.gyp
  14. AUTHORS
  15. BUILD.gn
  16. check_root_dir.py
  17. codereview.settings
  18. COPYING
  19. DEPS
  20. LICENSE
  21. license_template.txt
  22. LICENSE_THIRD_PARTY
  23. OWNERS
  24. PATENTS
  25. PRESUBMIT.py
  26. pylintrc
  27. README.md
  28. setup_links.py
  29. sync_chromium.py
  30. WATCHLISTS
README.md

WebRTC is a free, open software project that provides browsers and mobile applications with Real-Time Communications (RTC) capabilities via simple APIs. The WebRTC components have been optimized to best serve this purpose.

Our mission: To enable rich, high-quality RTC applications to be developed for the browser, mobile platforms, and IoT devices, and allow them all to communicate via a common set of protocols.

The WebRTC initiative is a project supported by Google, Mozilla and Opera, amongst others. This page is maintained by the Google Chrome team.

Development

See http://www.webrtc.org/native-code/development for instructions on how to get started developing with the native code.

More info