Revert "update calvo_addon note"

This reverts commit 3c51d8d.

Author: mmcky

lectures/_toc.yml

@@ -67,7 +67,6 @@ parts:
   - file: dyn_stack
   - file: calvo_machine_learn
   - file: calvo
-  - file: calvo_addon
   - file: opt_tax_recur
   - file: amss
   - file: amss2