Remove effect-less code

src/TechTreeImproved.cpp

@@ -216,7 +216,6 @@ bool TechTreeImproved::LoadData() {
 
 const std::vector<BuildDescription> & TechTreeImproved::HowToBuild(sc2::UnitTypeID unit) const
 {
-    sc2::UNIT_TYPEID unit_id = static_cast<sc2::UNIT_TYPEID>(unit);
     if (result_to_data.count(unit) > 0)
     {
         return result_to_data.at(unit);