Cleanup: Removes redundant includes on message_queue.h

This is part of a CL series merging rtc::MessageQueue into rtc::Thread.

Bug: webrtc:9883
Change-Id: I3cb857cc707d5e897759366d1478cc1ec19bce9a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/165344
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30180}
diff --git a/rtc_base/stream.h b/rtc_base/stream.h
index 9147dad..bfb9dc2 100644
--- a/rtc_base/stream.h
+++ b/rtc_base/stream.h
@@ -17,9 +17,9 @@
 #include "rtc_base/constructor_magic.h"
 #include "rtc_base/critical_section.h"
 #include "rtc_base/message_handler.h"
-#include "rtc_base/message_queue.h"
 #include "rtc_base/system/rtc_export.h"
 #include "rtc_base/third_party/sigslot/sigslot.h"
+#include "rtc_base/thread.h"
 
 namespace rtc {
 
@@ -49,8 +49,6 @@
 //  SE_WRITE: Data can be written, so Write is likely to not return SR_BLOCK
 enum StreamEvent { SE_OPEN = 1, SE_READ = 2, SE_WRITE = 4, SE_CLOSE = 8 };
 
-class Thread;
-
 struct StreamEventData : public MessageData {
   int events, error;
   StreamEventData(int ev, int er) : events(ev), error(er) {}