Bill Fellows explains how to find SSIS packages still using the Configuration option in the classic deployment model:
Create an SSIS package. Add a Variable to your package called FolderSource and assign it the path to your SSIS packages. Add a Script Task to the package and then add @[User::FolderSource] to the ReadOnly parameters.
Double click the script, assuming C#, and when it opens up, use the following script as your Main
Bill continues on with the contents of his script task, so click through for more.