cros: Disable new wallpaper picker for M69

The plan is to ship all tablet features together in M70. This CL will
be merged to M69 and reverted in M70.

Bug: 800945
Change-Id: I8ca2adb4b8b0c1715d7229f48bb521d0dd3ed35b
Reviewed-on: https://chromium-review.googlesource.com/1198523Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Wenzhao (Colin) Zang <wzang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587898}

ash/public/cpp/ash_features.cc

@@ -36,7 +36,7 @@ const base::Feature kLockScreenHideSensitiveNotificationsSupport{
     base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kNewWallpaperPicker{"NewWallpaperPicker",
-                                        base::FEATURE_ENABLED_BY_DEFAULT};
+                                        base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kNightLight{"NightLight", base::FEATURE_ENABLED_BY_DEFAULT};