Documentation Updates

# Required:
------------

This Issue continues the ongoing documentation work and is meant to capture low hanging fruit regarding correctness and out of date information.

- [ ] Remove references in C++ API : Any and Optional which is found [here](https://opentimelineio.readthedocs.io/en/stable/cxx/cxx.html):
- [ ] Decide how to handle out of date documentation / legacy information that does not reflect current information [See 1](https://opentimelineio.readthedocs.io/en/stable/cxx/cxx.html#proposed-otio-c-header-files) [and 2](https://github.com/AcademySoftwareFoundation/OpenTimelineIO/blob/main/docs/cxx/older.md)
- [ ] Remove duplication of information in the current documentation in main (see Python API and class lists)

Start by reviewing the linked C++ API page and docs/cxx/older.md, then compare the current documentation's Python API and class lists for duplicated or outdated information. Decide how legacy material should be handled and update the identified documentation so it no longer contains incorrect references or unnecessary duplication.

Written by the indexing model from the issue text.