Revert of Add Metal video view in AppRTCMobile and metal availability macro. (patchset #5 id:80001 of https://codereview.webrtc.org/2722583002/ )

Reason for revert:
Breaks AppRTCMobile

Original issue's description:
> Add Metal video view in AppRTCMobile and Metal availability macro.
>
> - The RTC_SUPPORTS_METAL macro allows consumers to gracefully handle compilation for different archs that are not supporting Metal.
>
> BUG=webrtc:7079
>
> Review-Url: https://codereview.webrtc.org/2722583002
> Cr-Commit-Position: refs/heads/master@{#17004}
> Committed: https://chromium.googlesource.com/external/webrtc/+/154a7bb877abefada22afe28b0a755cf621e8d9e

TBR=magjed@webrtc.org,tkchin@webrtc.org,denicija@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:7079

Review-Url: https://codereview.webrtc.org/2739793003
Cr-Commit-Position: refs/heads/master@{#17119}
4 files changed
tree: 9b4cd32e6bab5b5600be13e491bb9851d67eb198
  1. build_overrides/
  2. data/
  3. infra/
  4. resources/
  5. tools-webrtc/
  6. webrtc/
  7. .clang-format
  8. .git-blame-ignore-revs
  9. .gitignore
  10. .gn
  11. AUTHORS
  12. BUILD.gn
  13. check_root_dir.py
  14. cleanup_links.py
  15. codereview.settings
  16. DEPS
  17. LICENSE
  18. license_template.txt
  19. LICENSE_THIRD_PARTY
  20. OWNERS
  21. PATENTS
  22. PRESUBMIT.py
  23. pylintrc
  24. README.md
  25. 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