fix(core): Removes 6017 handler (#411)

- [X] Removes 6017 handler since it is only used in one place
- [X] Exposes a ref int to modify the packet length. This is acceptable since we technically have access to the entire reader/buffer.

Projects/Server/Network/Packets/IncomingMovementPackets.cs

@@ -78,7 +78,7 @@ namespace Server.Network
             ns.SendTimeSyncResponse();
         }
 
-        public static void MovementReq(NetState state, CircularBufferReader reader)
+        public static void MovementReq(NetState state, CircularBufferReader reader, ref int packetLength)
         {
             var from = state.Mobile;