Bump to WebRTC M131 release

Ongoing fixes and improvements, transient suppressor is gone. Also,
dropping isac because it doesn't seem to be useful, and is just build
system deadweight now.

Upstream references:

  Version: 131.0.6778.200
  WebRTC: 79aff54b0fa9238ce3518dd9eaf9610cd6f22e82
  Chromium: 2a19506ad24af755f2a215a4c61f775393e0db42

webrtc/rtc_base/event.h

@@ -58,6 +58,8 @@ class Event {
   // TODO(bugs.webrtc.org/14366): Consider removing this redundant alias.
   static constexpr webrtc::TimeDelta kForever =
       webrtc::TimeDelta::PlusInfinity();
+  static constexpr webrtc::TimeDelta kDefaultWarnDuration =
+      webrtc::TimeDelta::Seconds(3);
 
   Event();
   Event(bool manual_reset, bool initially_signaled);
@@ -83,7 +85,7 @@ class Event {
   // Waits with the given timeout and a reasonable default warning timeout.
   bool Wait(webrtc::TimeDelta give_up_after) {
     return Wait(give_up_after, give_up_after.IsPlusInfinity()
-                                   ? webrtc::TimeDelta::Seconds(3)
+                                   ? kDefaultWarnDuration
                                    : kForever);
   }