[Settings] Fix unable to accessing Fi

1. Get subscription ID from intent
2. Application context for proxy SubscriptionManager (since this is singleton)

Bug: 144172733
Test: Manual
Change-Id: I2f49d55da3380adeb40e8ff9414057113cb4ac35

src/com/android/settings/network/ProxySubscriptionManager.java

@@ -35,8 +35,7 @@ import java.util.List;
 /**
  * A proxy to the subscription manager
  */
-public class ProxySubscriptionManager extends SubscriptionManager.OnSubscriptionsChangedListener
-        implements LifecycleObserver {
+public class ProxySubscriptionManager implements LifecycleObserver {
 
     /**
      * Interface for monitor active subscriptions list changing
@@ -65,7 +64,7 @@ public class ProxySubscriptionManager extends SubscriptionManager.OnSubscription
         if (sSingleton != null) {
             return sSingleton;
         }
-        sSingleton = new ProxySubscriptionManager(context);
+        sSingleton = new ProxySubscriptionManager(context.getApplicationContext());
         return sSingleton;
     }
 
@@ -110,12 +109,6 @@ public class ProxySubscriptionManager extends SubscriptionManager.OnSubscription
         }
     }
 
-    @Override
-    public void onSubscriptionsChanged() {
-        clearCache();
-        notifyAllListeners();
-    }
-
     /**
      * Lifecycle for data within proxy
      *