Make Telephony related PreferenceController un-sliceable

Since the structure of Telephony is changed, some of Telephony
related PreferenceController cannot be converted to slices
smoothly whether devices have mobile data or not. So we
decided to make them un-sliceable.

Bug: 155846002
Test: robotests, manual
1. Settings -> Settings search -> search for roaming
2. Check that roaming result has no toggle widget.
Change-Id: I7cba8f6a750d9780a59411942665f68dac61248c

src/com/android/settings/network/telephony/TelephonyTogglePreferenceController.java

@@ -59,6 +59,11 @@ public abstract class TelephonyTogglePreferenceController extends TogglePreferen
         mSetSessionCount.getAndDecrement();
     }
 
+    @Override
+    public boolean isSliceable() {
+        return false;
+    }
+
     /**
      * Get carrier config based on specific subscription id.
      *