`get_quadratic_approximation_of_cubic` should also use `bezier` and `classic_bezier` should be removed

[behackl]

The implementation of get_quadratic_approximation_of_cubic caused some headache: when I tried to replace the current implementation of bezier, a test using get_quadratic_approximation_of_cubic started to fail because the points used in that function are not just 1d-numpy arrays as usual, but instead 2d ones. If someone wants to take a stab at fixing this, please go ahead -- then this classic_bezier function could also just be removed.

Originally posted by @behackl in #2421 (comment)

[chopan050]

PR #3829 had the side effect of removing calls to bezier inside get_quadratic_approximation_of_cubic. Thus, in the future, if someone wants to continue with PR #2421, they should now be able to rewrite the bezier function without having to move the old code into classic_bezier.

I'm closing this issue.