Revert "Wires up WebrtcKeyValueBasedConfig in media engines."

This reverts commit 591b2ab82ead157b5f5a85d5082bd15fe8c51809.

Reason for revert: Breaks downstream project

Original change's description:
> Wires up WebrtcKeyValueBasedConfig in media engines.
> 
> This replaces field_trial:: -based functions from system_wrappers.
> Field trials are still used as fallback, but injectable trials are now
> possible.
> 
> Bug: webrtc:11926
> Change-Id: I70f28c4fbabf6d9e55052342000e38612b46682c
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/174261
> Reviewed-by: Per Kjellander <perkj@webrtc.org>
> Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Reviewed-by: Stefan Holmer <stefan@webrtc.org>
> Reviewed-by: Sebastian Jansson <srte@webrtc.org>
> Commit-Queue: Erik Språng <sprang@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#32129}

TBR=mbonadei@webrtc.org,kthelgason@webrtc.org,sprang@webrtc.org,stefan@webrtc.org,srte@webrtc.org,perkj@webrtc.org

Change-Id: I3e169149a8b787aa6366bb357abb71794534c63a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:11926
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/184507
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32132}

sdk/BUILD.gn

@@ -973,7 +973,6 @@ if (is_ios || is_mac) {
         "../api/crypto:frame_encryptor_interface",
         "../api/rtc_event_log:rtc_event_log_factory",
         "../api/task_queue:default_task_queue_factory",
-        "../api/transport:field_trial_based_config",
         "../api/video:video_frame",
         "../api/video:video_rtp_headers",
         "../api/video_codecs:video_codecs_api",