Remove ash-disable-launcher-per-display flag

ash/wm/ash_activation_controller.cc

Index: ash/wm/ash_activation_controller.cc
diff --git a/ash/wm/ash_activation_controller.cc b/ash/wm/ash_activation_controller.cc
index f8c338a17815ea4e36514bac595be0ac2fd4207a..2c0237494e61eef948ec29c5f6f28300816dccc2 100644
--- a/ash/wm/ash_activation_controller.cc
+++ b/ash/wm/ash_activation_controller.cc
@@ -96,9 +96,7 @@ aura::Window* AshActivationController::PrepareToActivateLauncher() {
   if (!Shell::GetInstance()->delegate()->IsSpokenFeedbackEnabled())
     return NULL;
   ShelfWidget* shelf = GetRootWindowController(
-      Shell::IsLauncherPerDisplayEnabled() ?
-          Shell::GetActiveRootWindow() :
-          Shell::GetPrimaryRootWindow())->shelf();
+      Shell::GetActiveRootWindow())->shelf();
   // Launcher's window may be already destroyed in shutting down process.
   if (!shelf)
     return NULL;