message: Remove tau_ext from Cartesian impedance example
  Although tau_ext increases compliance significantly (similar to zero g mode)
  it can be confusing and not completely correct.
diff: @@ -148,7 +148,6 @@ void CartesianImpedanceExampleController::update(const ros::Time& /*time*/,
  Eigen::Map<Eigen::Matrix<double, 6, 7> > jacobian(jacobian_array.data());
  Eigen::Map<Eigen::Matrix<double, 7, 1> > q(robot_state.q.data());
  Eigen::Map<Eigen::Matrix<double, 7, 1> > dq(robot_state.dq.data());
  - Eigen::Map<Eigen::Matrix<double, 7, 1> > tau_ext(robot_state.tau_ext_hat_filtered.data());
  Eigen::Map<Eigen::Matrix<double, 7, 1> > tau_J_d( // NOLINT (readability-identifier-naming)
  robot_state.tau_J_d.data());
  Eigen::Affine3d transform(Eigen::Matrix4d::Map(robot_state.O_T_EE.data()));
  @@ -186,7 +185,7 @@ void CartesianImpedanceExampleController::update(const ros::Time& /*time*/,
  (nullspace_stiffness_ * (q_d_nullspace_ - q) -
  (2.0 * sqrt(nullspace_stiffness_)) * dq);
  // Desired torque
  - tau_d << tau_task + tau_nullspace + coriolis - tau_ext;
  + tau_d << tau_task + tau_nullspace + coriolis;
  // Saturate torque rate to avoid discontinuities
  tau_d << saturateTorqueRate(tau_d, tau_J_d, gravity);
  for (size_t i = 0; i < 7; ++i) {
  