Fix up-navigation for different levels of Settings screens.

No up affordance for 2-pane screens since there's already
a fragment breadcrumb for navigating up.

Bug: 6452961

Change-Id: Iad9a5c2d0b68cc8f2aec7d5ed8e2ab14d023d48c

src/com/android/settings/SubSettings.java

@@ -21,4 +21,10 @@ package com.android.settings;
  * since for our app it is a special singleTask class.
  */
 public class SubSettings extends Settings {
+
+    @Override
+    public boolean onNavigateUp() {
+        finish();
+        return true;
+    }
 }