Revert "Add about flag for enabling the PipeWire support in WebRTC"

This reverts commit 8788015d2b2efa354c641f4e0ed38fba726f3ae7.

Reason for revert: This change is not complete, because it makes some unit tests to fail (this was found during the WebRTC roll). It's safer to revert this and let the WebRTC roll succeed and then fix the unit tests.

Original change's description:
> Add about flag for enabling the PipeWire support in WebRTC
>
> Add a new enable-webrtc-pipewire-capturer about flag, that when
> enabled, will allow to use the PipeWire media server for providing
> the screen content for screen casting when user is running on Wayland
> display server on Linux.
>
> The flag is disabled by default, due to the user experience as it
> involves two extra confirmation dialogs outside of Chromium - requested
> by Weiyong Yao. It could change the default, once it goes through Chromium
> UI review.
>
> Bug: 682122
> Change-Id: I70c07a4a170b2bf1717f6c155905625eba84ff5a
> Reviewed-on: https://chromium-review.googlesource.com/c/1365444
> Reviewed-by: Weiyong Yao <braveyao@chromium.org>
> Reviewed-by: Jochen Eisinger <jochen@chromium.org>
> Commit-Queue: Tomáš Popela <tomas.popela@gmail.com>
> Cr-Commit-Position: refs/heads/master@{#615886}

TBR=braveyao@chromium.org,jochen@chromium.org,tomas.popela@gmail.com

Bug: 682122
Change-Id: I71376def29423accafe94344c9a385ff4a038df5
Reviewed-on: https://chromium-review.googlesource.com/c/1379756
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620075}
9 files changed