do you get this in a custom module after you have completed migration?
The assembly Telerik.Cms.Web is a 3.7 assembly and is no longer part of Sitefinity 4. If your custom module or controls make use of those namespaces, you'll need to update your code to use the new Sitefinity API.
the sitefintiy documentation
has many articles with sample code, but if you have any specific questions let me know and I'll try to help!
hope this is helpful!