Delete old name ProcessAllMessageQueues

Bug: webrtc:10198
Change-Id: I5aca69101e6f70080b3209ebabf0007d82114632
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/179482
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31832}

rtc_base/thread.h

@@ -82,9 +82,6 @@ class RTC_EXPORT ThreadManager {
   static void Remove(Thread* message_queue);
   static void Clear(MessageHandler* handler);
 
-  // TODO(nisse): Delete alias, as soon as downstream code is updated.
-  static void ProcessAllMessageQueues() { ProcessAllMessageQueuesForTesting(); }
-
   // For testing purposes, for use with a simulated clock.
   // Ensures that all message queues have processed delayed messages
   // up until the current point in time.