Refacotr mobile data observer for repository

In current design, the mobile data observer might be removed due to
SIM absence after registered so that mobile data network info can't
be updated to clients.

To fix it, migrate it to use API TelephonyCallback.onUserMobileDataStateChanged
Bug: 327696232

Change-Id: I26c8f946823abb7505f0227c8dd8ab0700d0c5f2

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

@@ -100,9 +100,6 @@ public abstract class DefaultSubscriptionController extends TelephonyBasePrefere
         mMobileNetworkRepository.addRegister(mLifecycleOwner, this,
                 SubscriptionManager.INVALID_SUBSCRIPTION_ID);
         mMobileNetworkRepository.updateEntity();
-        // Can not get default subId from database until get the callback, add register by subId
-        // later.
-        mMobileNetworkRepository.addRegisterBySubId(getDefaultSubscriptionId());
         mDataSubscriptionChangedReceiver.registerReceiver();
     }