[LockSetup] Hide back button in notification interstitial

The back button is disabled because the lock screen is already set
up. Per UX spec, we should hide the back button instead of disabling
it.

Bug: 20427092
Change-Id: Iaaf8860208179dfa5974b172013f9882827c6c4a

src/com/android/settings/SetupRedactionInterstitial.java

@@ -28,6 +28,7 @@ import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
+import android.widget.Button;
 
 /**
  * Setup Wizard's version of RedactionInterstitial screen. It inherits the logic and basic structure
@@ -82,7 +83,8 @@ public class SetupRedactionInterstitial extends RedactionInterstitial {
 
             final NavigationBar navigationBar = layout.getNavigationBar();
             navigationBar.setNavigationBarListener(this);
-            navigationBar.getBackButton().setEnabled(false);
+            final Button backButton = navigationBar.getBackButton();
+            backButton.setVisibility(View.GONE);
             SetupWizardUtils.setImmersiveMode(getActivity());
             return layout;
         }