Remove comment.

Change-Id: Id4e254b78049373025d52dd1d04ecfc0f53c8e8e
Reviewed-on: https://chromium-review.googlesource.com/911881Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537762}

third_party/WebKit/Source/core/html/media/PictureInPictureInterstitial.h

@@ -12,7 +12,6 @@ namespace blink {
 
 class HTMLImageElement;
 class HTMLVideoElement;
-// class PictureInPictureMessageElement;
 
 // Picture in Picture UI. DOM structure looks like:
 //