Remove virtual inheritance from RTCStatsCollector

Bug: none
Change-Id: I5c3d93f3cc64c588c2f8e750c70c51c991736023
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215961
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33814}
diff --git a/api/stats/rtc_stats_collector_callback.h b/api/stats/rtc_stats_collector_callback.h
index c3e0824..506cc63 100644
--- a/api/stats/rtc_stats_collector_callback.h
+++ b/api/stats/rtc_stats_collector_callback.h
@@ -17,7 +17,7 @@
 
 namespace webrtc {
 
-class RTCStatsCollectorCallback : public virtual rtc::RefCountInterface {
+class RTCStatsCollectorCallback : public rtc::RefCountInterface {
  public:
   ~RTCStatsCollectorCallback() override = default;