CrOS GMC: Remove unnecessary dcheck.

This CL removes the DCHECK for pin state in media controls detailed
view since we are not removing media controls from system menu
immediately after user pinned media controls. So user can tap the
media controls again while the system menu is still open and get
back to the detailed view with the media controls pinned to shelf.

Change-Id: I60235836686b535c0a06ee0bf99e97141ba9bf80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435560Reviewed-by: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Commit-Queue: Jazz Xu <jazzhsu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811539}

ash/system/media/unified_media_controls_detailed_view.cc

@@ -25,10 +25,6 @@ UnifiedMediaControlsDetailedView::UnifiedMediaControlsDetailedView(
 }
 
 void UnifiedMediaControlsDetailedView::CreateExtraTitleRowButtons() {
-  // DetailedView should only be visible when global media controls
-  // is NOT pinned to shelf.
-  DCHECK(!MediaTray::IsPinnedToShelf());
-
   tri_view()->SetContainerVisible(TriView::Container::END, true);
   tri_view()->AddView(TriView::Container::END, new MediaTray::PinButton());
 }