remove unnecessary references.md and appendix (not needed in jupyter-book)

Author: trevorcampbell

source/_toc.yml

@@ -23,6 +23,3 @@ parts:
     - file: inference.md
     - file: jupyter.md
     - file: version-control.md
-#- caption: Appendix
-#  chapters:
-#    - file: references.md