Fix tutorial documentation errors and inconsistencies

getting_started.md:
- Fix invalid level='cma' → level='CMA' (line 157)
- Fix invalid regions key 'cma' → 'CMA' (line 157)
- Remove emoji from "Key Improvement" section

caching_data.md:
- Complete rewrite to use only actual pycancensus API functions
- Replace non-existent list_cached_data() with list_cache()
- Remove all references to non-existent remove_cached_data()
- Focus on real cache functions: list_cache(), remove_from_cache(), clear_cache()
- Add proper examples using get_cache_path(), set_cache_path()
- All code examples now match the actual API

Both tutorials now execute successfully in Sphinx build.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: dshkol