Remove dead code: updateUpstreamIPv6LinkProperties in InitialState

mRaemon only be created at BaseServingState#enter() and set to null at
BaseServingState#exit(). Thus, updateUpstreamIPv6LinkProperties just be
no-op in InitialState.

Test: atest TetheringTests MtsTetheringTestLatestSdk CtsTetheringTest
Change-Id: I0b8403a2acffb1aa0f40d2ad8721d4eff7c63ff0

Tethering/src/android/net/ip/IpServer.java

@@ -1146,9 +1146,6 @@ public class IpServer extends StateMachine {
                 case CMD_INTERFACE_DOWN:
                     transitionTo(mUnavailableState);
                     break;
-                case CMD_IPV6_TETHER_UPDATE:
-                    updateUpstreamIPv6LinkProperties((LinkProperties) message.obj, message.arg1);
-                    break;
                 default:
                     return NOT_HANDLED;
             }