To get rid of it you can shift+MMD the motion path node and the node of the object that's attached to the motion path, this will open up the Connection Editor. On the motion path node side, expand 'allCoordinates' and on the constrained node expand 'translate'. Now connect the 'xCoordinate' from the left to the 'translateX' on the right. Do the same for Y and Z. Now you can delete the addDoubleLinear node.