make parametric-curves deprecated.

[proyan]

Currently humanoid-path-plannar/hpp-spline and sot/parametric-curves are both implementing curves of the form f(t). As discussed in stack-of-tasks/parametric-curves#12, hpp-spline is an easier alternative for future team projects.

As a result, parametric-curves needs to be made deprecated and eventually replaced with hpp-spline. Currently hpp-spline does not have all the trajectories that have been implemented in parametric-curves. Once that happen, this issue should be dealt with.