Gut ash::MaterialDesignController, and remove the about:flags entry.

ash/common/ash_switches.cc

Index: ash/common/ash_switches.cc
diff --git a/ash/common/ash_switches.cc b/ash/common/ash_switches.cc
index 37ac6b3afa44da2176fd8da3334a9df195a0feb5..877bc571a5775a00e9cbe4ea207df02d5ec8ad24 100644
--- a/ash/common/ash_switches.cc
+++ b/ash/common/ash_switches.cc
@@ -73,13 +73,6 @@ const char kAshForceEnablePalette[] = "ash-force-enable-palette";
 const char kAshHideNotificationsForFactory[] =
     "ash-hide-notifications-for-factory";
 
-// Specifies if Material Design elements in Chrome OS system UI are enabled.
-// Can be disabled / enabled / experimental allowing to launch incrementally.
-const char kAshMaterialDesign[] = "ash-md";
-const char kAshMaterialDesignDisabled[] = "disabled";
-const char kAshMaterialDesignEnabled[] = "enabled";
-const char kAshMaterialDesignExperimental[] = "experimental";
-
 // Enables the heads-up display for tracking touch points.
 const char kAshTouchHud[] = "ash-touch-hud";