Revert "Enable use of rtc::SystemTimeNanos() provided by Chromium"

This reverts commit dfe19719e53abfd4d73722942445c5e1046b671b.

Reason for revert: Breaks fuzzers in Chromium builds. See https://ci.chromium.org/ui/p/chromium/builders/try/linux-libfuzzer-asan-rel/685438/overview. I am reverting since this blocks the roll but I will be in touch for a fix.

Original change's description:
> Enable use of rtc::SystemTimeNanos() provided by Chromium
>
> This is the third CL out of three to enable overriding
> of the function SystemTimeNanos() in rtc_base/system_time.cc
>
> When WebRTC is built as part of Chromium the rtc::SystemTimeNanos()
> function provided by Chromium will be used. This is controlled
> by the build argument rtc_exclude_system_time which directly
> maps to the macro WEBRTC_EXCLUDE_SYSTEM_TIME.
>
> By doing this we are making sure that the WebRTC and Chromium
> clocks are the same.
>
> Bug: chromium:516700
> Change-Id: If7f749c4aadefb1cfc07ba4c7e3f45dc6c31118b
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/208223
> Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#33337}

TBR=kron@webrtc.org

Bug: chromium:516700
Change-Id: I9ecd1784a6c1cdac8bae07d34f7df20c62a21a95
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/208740
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33340}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 32ef93e..28ff7fd 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -407,10 +407,6 @@
     ":stringutils",
     "system:rtc_export",
   ]
-  if (rtc_exclude_system_time) {
-    defines = [ "WEBRTC_EXCLUDE_SYSTEM_TIME" ]
-  }
-
   libs = []
   if (is_win) {
     libs += [ "winmm.lib" ]
diff --git a/rtc_base/system_time.cc b/rtc_base/system_time.cc
index 9efe76e..bcd4e6c 100644
--- a/rtc_base/system_time.cc
+++ b/rtc_base/system_time.cc
@@ -8,10 +8,6 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-// If WEBRTC_EXCLUDE_SYSTEM_TIME is set, an implementation of
-// rtc::SystemTimeNanos() must be provided externally.
-#ifndef WEBRTC_EXCLUDE_SYSTEM_TIME
-
 #include <stdint.h>
 
 #include <limits>
@@ -94,4 +90,3 @@
 }
 
 }  // namespace rtc
-#endif  // WEBRTC_EXCLUDE_SYSTEM_TIME
diff --git a/rtc_tools/BUILD.gn b/rtc_tools/BUILD.gn
index 2020957..f6352d8 100644
--- a/rtc_tools/BUILD.gn
+++ b/rtc_tools/BUILD.gn
@@ -136,12 +136,6 @@
     "//third_party/abseil-cpp/absl/flags:parse",
     "//third_party/abseil-cpp/absl/strings",
   ]
-
-  if (build_with_chromium) {
-    # When building from Chromium, WebRTC's metrics and field trial
-    # implementations need to be replaced by the Chromium ones.
-    deps += [ "//third_party/webrtc_overrides:webrtc_component" ]
-  }
 }
 
 # TODO(bugs.webrtc.org/11474): Enable this on win if needed. For now it
diff --git a/webrtc.gni b/webrtc.gni
index c1227ba..08b2d66 100644
--- a/webrtc.gni
+++ b/webrtc.gni
@@ -63,7 +63,7 @@
   # will tell the pre-processor to remove the default definition of the
   # SystemTimeNanos() which is defined in rtc_base/system_time.cc. In
   # that case a new implementation needs to be provided.
-  rtc_exclude_system_time = build_with_chromium
+  rtc_exclude_system_time = false
 
   # Setting this to false will require the API user to pass in their own
   # SSLCertificateVerifier to verify the certificates presented from a