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/AppMemoryPreferenceController.java

@@ -17,7 +17,6 @@
 package com.android.settings.applications.appinfo;
 
 import android.app.Activity;
-import android.app.slice.Slice;
 import android.content.Context;
 import android.content.pm.PackageInfo;
 import android.os.AsyncTask;
@@ -110,11 +109,6 @@ public class AppMemoryPreferenceController extends BasePreferenceController
                 ? AVAILABLE : DISABLED_DEPENDENT_SETTING;
     }
 
-    @Override
-    public Slice getSettingSlice() {
-        return null;
-    }
-
     @Override
     public void displayPreference(PreferenceScreen screen) {
         super.displayPreference(screen);