[Enhancement] Remove robotcode.python setting

[d-biehl]

Remove robotcode.python setting, it is already deprecated.

Yes, this is an old setting and comes from a time when the Python extension did not have a public API. It should normally no longer be used. See here for an explanation.

I will deprecate the robotcode.python setting in the next version and then remove it after a while. I am not sure yet if it is necessary to provide a replacement for it, since python provides the python.defaultInterpreterPath.

Originally posted by @d-biehl in #222 (comment)