ui: Cleanup class/struct forward declarations

ui/ozone/platform/drm/gpu/drm_thread.h

Index: ui/ozone/platform/drm/gpu/drm_thread.h
diff --git a/ui/ozone/platform/drm/gpu/drm_thread.h b/ui/ozone/platform/drm/gpu/drm_thread.h
index cdf914828916ae1cc17a6764495eea4eab8a274c..8b8743b7640b5a50e72a74285d8a9b6698eec480 100644
--- a/ui/ozone/platform/drm/gpu/drm_thread.h
+++ b/ui/ozone/platform/drm/gpu/drm_thread.h
@@ -31,16 +31,10 @@ class Point;
 class Rect;
 }
 
-namespace service_manager {
-class Connection;
-}
-
 namespace ui {
 
 class DrmDeviceManager;
 class DrmGpuDisplayManager;
-class DrmWindow;
-class DrmWindowProxy;
 class GbmBuffer;
 class ScanoutBufferGenerator;
 class ScreenManager;