feat: automatically remove queued messages with stale locks (#2872)

app/lib/message_dequeuer/initial_processor.rb

@@ -29,8 +29,8 @@ module MessageDequeuer
     private
 
     def check_message_exists
-      @queued_message.message
-    rescue Postal::MessageDB::Message::NotFound
+      return if @queued_message.message
+
       log "unqueue because backend message has been removed."
       remove_from_queue
       stop_processing