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
diff --git a/Tethering/src/android/net/ip/IpServer.java b/Tethering/src/android/net/ip/IpServer.java
index 438b592..0a34669 100644
--- a/Tethering/src/android/net/ip/IpServer.java
+++ b/Tethering/src/android/net/ip/IpServer.java
@@ -1146,9 +1146,6 @@
                 case CMD_INTERFACE_DOWN:
                     transitionTo(mUnavailableState);
                     break;
-                case CMD_IPV6_TETHER_UPDATE:
-                    updateUpstreamIPv6LinkProperties((LinkProperties) message.obj, message.arg1);
-                    break;
                 default:
                     return NOT_HANDLED;
             }