Merge ash/public/cpp/ash_features.* into ash/constants/

ash/{public/cpp,constants}/ash_features.* serve the same purpose. The
latter is now the proper directory to add features to.

Bug: 1164001
Change-Id: I8f97e21af631b72996df5e9df142692fe32b2595
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2949052
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#892994}

diff --git a/ash/drag_drop/tab_drag_drop_delegate.cc b/ash/drag_drop/tab_drag_drop_delegate.cc
index 1d337426..47ca61e 100644
--- a/ash/drag_drop/tab_drag_drop_delegate.cc
+++ b/ash/drag_drop/tab_drag_drop_delegate.cc

@@ -4,7 +4,7 @@
 
 #include "ash/drag_drop/tab_drag_drop_delegate.h"
 
-#include "ash/public/cpp/ash_features.h"
+#include "ash/constants/ash_features.h"
 #include "ash/public/cpp/presentation_time_recorder.h"
 #include "ash/public/cpp/window_properties.h"
 #include "ash/screen_util.h"