Delete unneeded references to EventWrapper.

Bug: None
Change-Id: Id29128e6f70ca72db9bc5aa604b015829f98e272
Reviewed-on: https://webrtc-review.googlesource.com/70141
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22896}

common_video/incoming_video_stream.cc

@@ -15,7 +15,6 @@
 #include "common_video/video_render_frames.h"
 #include "rtc_base/timeutils.h"
 #include "rtc_base/trace_event.h"
-#include "system_wrappers/include/event_wrapper.h"
 
 namespace webrtc {
 namespace {

test/frame_generator_capturer.h

@@ -22,8 +22,6 @@
 
 namespace webrtc {
 
-class EventTimerWrapper;
-
 namespace test {
 
 class FrameGenerator;