Remove undocumented page
We're not keeping this page up to date, so it's only a small
portion of undocumented content. This is misleading because it
makes readers think that this is the only information not
documented.
- [Appendices](appendices.md)
- [Macro Follow-Set Ambiguity Formal Specification](macro-ambiguity.md)
- [Influences](influences.md)
- - [As-Yet-Undocumented Features](undocumented.md)
- [Glossary](glossary.md)
