Remove workarounds to use core platform API

Core platform API stubs are now correctly included in module_current and
system_server_current, so workarounds used to use such APIs can be
removed.

OsCompat and InetAddressCompat were only necessary because manually
adding the stubs did not resolve the problem for classes that had
public API stubs, which shadowed the module API stubs.

The manual stubs dependency was already removed in another change. Also
remove the service jar dependency on android_system_server_stubs_current
as it is already included in sdk_version system_server_current.

Bug: 183097033
Test: atest CtsNetTestCases

Change-Id: Id448be03b679f832edb24f1b77f471227faf5268

framework/src/android/net/ConnectivityManager.java

@@ -4939,7 +4939,7 @@ public class ConnectivityManager {
                 Log.e(TAG, "Can't set proxy properties", e);
             }
             // Must flush DNS cache as new network may have different DNS resolutions.
-            InetAddressCompat.clearDnsCache();
+            InetAddress.clearDnsCache();
             // Must flush socket pool as idle sockets will be bound to previous network and may
             // cause subsequent fetches to be performed on old network.
             NetworkEventDispatcher.getInstance().dispatchNetworkConfigurationChange();