Revert: udp-rlybuf option

As a low-level networking tool, tun2socks should be able to handle UDP packets of all possible sizes. This reverts commit fb9ca95909.

engine/engine.go

@@ -133,14 +133,6 @@ func general(k *Key) error {
 		}
 		tunnel.SetUDPTimeout(k.UDPTimeout)
 	}
-
-	if k.UDPRelayBufferSize != "" {
-		size, err := units.RAMInBytes(k.UDPRelayBufferSize)
-		if err != nil {
-			return err
-		}
-		tunnel.SetUDPRelayBufferSize(int(size))
-	}
 	return nil
 }