Improve 2 dof simulation code

..._2dof/simple_robot_2dof/forward_kinematics_node_2dof_1.py

..._2dof/simple_robot_2dof/forward_kinematics_node_2dof_2.py

...ot_2dof/simple_robot_2dof/inverse_kinematics_2dof_node.py