Fix dead links from side bar

Author: nicolasstucki

docs/docs/reference/dropped/delayedInit.md renamed to docs/docs/reference/dropped/delayed-init.md

@@ -11,8 +11,6 @@ sidebar:
           url: docs/usage/cbt-projects.html
         - title: Dottydoc
           url: docs/usage/dottydoc.html
-        - title: Migrating
-          url: docs/usage/migrating.html
     - title: Reference
       subsection:
         - title: New Types