Use fast unlocks impl

Author: nygrenh

app/models/unlock.rb

@@ -24,7 +24,7 @@ def self.refresh_unlocks(course, user)
     Unlock.transaction do
       unlocks = course.unlocks.where(user_id: user.id)
       by_exercise_name = Hash[unlocks.map { |u| [u.exercise_name, u] }]
-      refresh_unlocks_impl(course, user, by_exercise_name)
+      fast_refresh_unlocks_impl(course, user, by_exercise_name)
       UncomputedUnlock.where(course_id: course.id, user_id: user.id).where("created_at < ?", time).delete_all
     end
   end