Simulink Data Dictionary has the capability. You can migrate your workspace variables to a Simulink Data Dictionary. When you do the migration, it only migrates the variables that are used by the model. It will ask you whenther to clear those variables (that has been migrated to a SLDD) from the workspace. If you answer "Yes", then you will be left with a list of variables in the workspace that are not used by the model.
In your Simulink model, click File, Model Properties, Link to Data Dictionary,