Move webrtc/pc/media_stream_track.h

It's now in the API directory of third_party/webrtc

Bug: webrtc:11967
Change-Id: I752ffa3261fa4080bac565c58d544f900a0bd890
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2463609Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816530}

third_party/blink/renderer/platform/peerconnection/webrtc_audio_sink.h

@@ -24,7 +24,7 @@
 #include "third_party/blink/renderer/platform/platform_export.h"
 #include "third_party/blink/renderer/platform/wtf/cross_thread_copier.h"
 #include "third_party/webrtc/api/media_stream_interface.h"
-#include "third_party/webrtc/pc/media_stream_track.h"
+#include "third_party/webrtc/api/media_stream_track.h"
 #include "third_party/webrtc/rtc_base/time_utils.h"
 #include "third_party/webrtc/rtc_base/timestamp_aligner.h"