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/time_utils.h

@@ -129,11 +129,11 @@ int64_t TmToSeconds(const tm& tm);
 // system time is changed, e.g., by some other process calling
 // settimeofday. Always use rtc::TimeMicros(), not this function, for
 // measuring time intervals and timeouts.
-int64_t TimeUTCMicros();
+RTC_EXPORT int64_t TimeUTCMicros();
 
 // Return the number of milliseconds since January 1, 1970, UTC.
 // See above.
-int64_t TimeUTCMillis();
+RTC_EXPORT int64_t TimeUTCMillis();
 
 }  // namespace rtc