Only show one copy of each preference

Fixes: 37912144
Fixes: 37909560
Test: manual, load app settings for legacy and upgrade apps from
inline settings, click (i), and click back.

Change-Id: Ieb96cca03f2596fd44cd33facafa3d4af1fbc24d

src/com/android/settings/notification/AppNotificationSettings.java

@@ -91,6 +91,8 @@ public class AppNotificationSettings extends NotificationSettingsBase {
 
         if (getPreferenceScreen() != null) {
             getPreferenceScreen().removeAll();
+            mChannelGroups.clear();
+            mShowLegacyChannelConfig = false;
         }
 
         addPreferencesFromResource(R.xml.app_notification_settings);