Remove Slice getter from BasePreferenceController

After working through a prototype here: (ag/3324435)
it is clear that we don't need the controller to
provider the slice. We will build an index that
will contain sufficent UI information, and a reference
to the controller.

At Slice Bind time, we can get the curret value from the
controller, and the UI information from the Index.

Bug: 67996923
Test: robotests
Change-Id: Id43a51bcd73051bc719cd5829907583e0edf23b2

src/com/android/settings/applications/appinfo/DefaultAppShortcutPreferenceControllerBase.java

@@ -50,11 +50,6 @@ public abstract class DefaultAppShortcutPreferenceControllerBase extends BasePre
         return hasAppCapability() ? AVAILABLE : DISABLED_UNSUPPORTED;
     }
 
-    @Override
-    public Slice getSettingSlice() {
-        return null;
-    }
-
     @Override
     public void updateState(Preference preference) {
         preference.setSummary(isDefaultApp() ? R.string.yes : R.string.no);