docs: Remove useless page

Author: smarter

docs/docs/index.md

@@ -23,7 +23,6 @@ Contents
     - [Enum Translation](reference/desugarEnums.md)
     - [By-Name Implicits](reference/implicit-by-name-parameters.md)
 * Usage
-    - [Migrating from Scala 2](usage/migrating.md): migration information
     - [Dotty projects with sbt](usage/sbt-projects.md): using sbt
     - [IDE support for Dotty](usage/ide-support.md)
     - [Dotty projects with cbt](usage/cbt-projects.md): using cbt