Documentation fix: MonoBehaviour.OnAwake -> Awake (#3927)

`OnAwake` is not expected to exist and is thus never called

docs/Migrating.md

     data in the new MonoBehaviour instead.
   - If the class overrode the virtual methods, create a new MonoBehaviour and
     move the logic to it:
-    - Move the InitializeAcademy code to MonoBehaviour.OnAwake
+    - Move the InitializeAcademy code to MonoBehaviour.Awake
     - Move the AcademyStep code to MonoBehaviour.FixedUpdate
     - Move the OnDestroy code to MonoBehaviour.OnDestroy.
     - Move the AcademyReset code to a new method and add it to the