[cleanup] Remove useless includes.

Manual cleanup guided by include-what-you-use diagnostic.

Bug: webrtc:8311
Change-Id: I00be03392cc7ee005101427ea7dc701621ccea68
Reviewed-on: https://webrtc-review.googlesource.com/c/103320
Commit-Queue: Yves Gerey <yvesg@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25013}

sdk/objc/api/peerconnection/RTCVideoSource+Private.h

@@ -13,6 +13,7 @@
 #import "RTCMediaSource+Private.h"
 
 #include "api/mediastreaminterface.h"
+#include "rtc_base/thread.h"
 
 NS_ASSUME_NONNULL_BEGIN
 

sdk/objc/native/api/video_capturer.h

@@ -15,6 +15,7 @@
 
 #include "api/mediastreaminterface.h"
 #include "rtc_base/scoped_ref_ptr.h"
+#include "rtc_base/thread.h"
 
 namespace webrtc {