Use parameter list of Indiana refundable credits

In #2865 I hard-coded `adds = ["in_eitc", "in_unified_elderly_tax_credit"]` in the `in_refundable_credits` formula so that they display correctly in the app. Previously we used a formula that pulls in the list parameter, since the `in` keyword in the parameter path breaks `adds`.

Once we fix https://github.com/PolicyEngine/policyengine-core/issues/112 let's return to the parameter.