Fix unschedule_old_dynamic_tasks method

Author: cupatea

lib/solid_queue/scheduler/recurring_schedule.rb

@@ -38,7 +38,7 @@ def schedule_new_dynamic_tasks
     end
 
     def unschedule_old_dynamic_tasks
-      (scheduled_tasks.keys - dynamic_tasks.pluck(:key)).each do |key|
+      (scheduled_tasks.keys - SolidQueue::RecurringTask.pluck(:key)).each do |key|
         scheduled_tasks[key].cancel
         scheduled_tasks.delete(key)
       end