Remove deprecated field_trial_default and metrics_default.

This CL removes some deprecated build targets (and their headers)
from system_wrappers:
- field_trial_api
- field_trial_default
- metrics_api
- metrics_default

It also refreshes all the dependencies on field_trial.h and metrics.h.

A nice side effect is that it is finally possible to remove 'nogncheck'
from the following files (when it was used with field_trial_default
and metrics_default):
- sdk/objc/api/peerconnection/RTCMetricsSampleInfo+Private.h
- sdk/android/src/jni/pc/peerconnectionfactory.cc
- sdk/objc/api/peerconnection/RTCFieldTrials.mm

Bug: webrtc:9631
Change-Id: Ib621f41ef8ad0aba4fe1c1d7e749c044afc956c3
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/100524
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24878}
diff --git a/video/BUILD.gn b/video/BUILD.gn
index cecdd38..a26815b 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -79,8 +79,8 @@
     "../rtc_base/experiments:alr_experiment",
     "../rtc_base/experiments:quality_scaling_experiment",
     "../rtc_base/system:fallthrough",
-    "../system_wrappers:field_trial_api",
-    "../system_wrappers:metrics_api",
+    "../system_wrappers:field_trial",
+    "../system_wrappers:metrics",
     "//third_party/abseil-cpp/absl/memory",
     "//third_party/abseil-cpp/absl/types:optional",
 
@@ -175,7 +175,7 @@
     "../rtc_base:timeutils",
     "../rtc_base/experiments:quality_scaling_experiment",
     "../rtc_base/system:fallthrough",
-    "../system_wrappers:field_trial_api",
+    "../system_wrappers:field_trial",
     "//third_party/abseil-cpp/absl/types:optional",
   ]
 }
@@ -259,7 +259,7 @@
       "../modules/video_coding:webrtc_vp9",
       "../rtc_base:rtc_base_approved",
       "../rtc_base/experiments:alr_experiment",
-      "../system_wrappers:field_trial_default",
+      "../system_wrappers:field_trial",
       "../test:field_trial",
       "../test:test_common",
       "../test:test_support",
@@ -283,8 +283,7 @@
       ":video_quality_test",
       "../rtc_base:logging",
       "../rtc_base:rtc_base_approved",
-      "../system_wrappers:field_trial_default",
-      "../system_wrappers:metrics_default",
+      "../system_wrappers:field_trial",
       "../system_wrappers:runtime_enabled_features_default",
       "../test:field_trial",
       "../test:run_test",
@@ -310,8 +309,7 @@
       ":video_quality_test",
       "../rtc_base:logging",
       "../rtc_base:rtc_base_approved",
-      "../system_wrappers:field_trial_default",
-      "../system_wrappers:metrics_default",
+      "../system_wrappers:field_trial",
       "../system_wrappers:runtime_enabled_features_default",
       "../test:field_trial",
       "../test:run_test",
@@ -336,8 +334,7 @@
       ":video_quality_test",
       "../rtc_base:logging",
       "../rtc_base:rtc_base_approved",
-      "../system_wrappers:field_trial_default",
-      "../system_wrappers:metrics_default",
+      "../system_wrappers:field_trial",
       "../system_wrappers:runtime_enabled_features_default",
       "../test:field_trial",
       "../test:run_test",
@@ -369,10 +366,8 @@
       "../rtc_base:rtc_base_approved",
       "../rtc_base:rtc_json",
       "../system_wrappers",
-      "../system_wrappers:metrics_default",
       "../system_wrappers:runtime_enabled_features_default",
       "../test:fake_video_codecs",
-      "../test:field_trial",
       "../test:rtp_test_utils",
       "../test:run_test",
       "../test:run_test_interface",
@@ -479,9 +474,8 @@
       "../rtc_base:rtc_task_queue_for_test",
       "../rtc_base/experiments:alr_experiment",
       "../system_wrappers",
-      "../system_wrappers:field_trial_default",
-      "../system_wrappers:metrics_api",
-      "../system_wrappers:metrics_default",
+      "../system_wrappers:field_trial",
+      "../system_wrappers:metrics",
       "../test:direct_transport",
       "../test:fake_video_codecs",
       "../test:field_trial",