Change to use the expand button in support lib.

- functionality for hiding portions of the preferences in the preference
screen is added to the support lib. So, changing the settings
implementation to use the feature from the support lib instead.
- remove ProgressiveDisclosureMixin and the related code

Fixes: 63985174
Test: make RunSettingsRoboTests
Change-Id: Ib1d39b2db93d78a56c7adf90abcae5226f9564c2

src/com/android/settings/dashboard/DashboardFeatureProviderImpl.java

@@ -188,16 +188,6 @@ public class DashboardFeatureProviderImpl implements DashboardFeatureProvider {
         }
     }
 
-    @Override
-    public ProgressiveDisclosureMixin getProgressiveDisclosureMixin(Context context,
-            DashboardFragment fragment, Bundle args) {
-        boolean keepExpanded = false;
-        if (args != null) {
-            keepExpanded = args.getString(SettingsActivity.EXTRA_FRAGMENT_ARG_KEY) != null;
-        }
-        return new ProgressiveDisclosureMixin(context, fragment, keepExpanded);
-    }
-
     @Override
     public String getExtraIntentAction() {
         return null;