Remove usage of Context.NETWORK_STACK_SERVICE

The NetworkStack.getService() API should be used instead.

Bug: 151243982
Test: atest FrameworksNetTests TetheringTests
      Manual tethering test
Merged-In: I7855090bffbe895c8349ad4903b8f2eb55515f0b
(clean cherry-pick from internal branch)

Change-Id: If4af2846a82605e828287a9a4680d5547b76b802
diff --git a/tests/net/java/com/android/server/ConnectivityServiceTest.java b/tests/net/java/com/android/server/ConnectivityServiceTest.java
index 9dc0a62..4aa1b20 100644
--- a/tests/net/java/com/android/server/ConnectivityServiceTest.java
+++ b/tests/net/java/com/android/server/ConnectivityServiceTest.java
@@ -428,7 +428,6 @@
         public Object getSystemService(String name) {
             if (Context.CONNECTIVITY_SERVICE.equals(name)) return mCm;
             if (Context.NOTIFICATION_SERVICE.equals(name)) return mNotificationManager;
-            if (Context.NETWORK_STACK_SERVICE.equals(name)) return mNetworkStack;
             if (Context.USER_SERVICE.equals(name)) return mUserManager;
             if (Context.ALARM_SERVICE.equals(name)) return mAlarmManager;
             if (Context.LOCATION_SERVICE.equals(name)) return mLocationManager;