Fixup 1a25d297b8 (unused variable)

This function can likely be removed now, but I don't want to do it just yet.

src/statistics.cpp

@@ -535,7 +535,6 @@ void un_recruit_unit(const unit& u)
 
 int un_recall_unit_cost(const unit& u)  // this really belongs elsewhere, perhaps in undo.cpp
 {					// but I'm too lazy to do it at the moment
-	stats& s = get_stats(get_team_save_id(u));
 	return u.recall_cost();
 }