Make migrate stats faster and fix missing delete

api/migrate_stats.sql

 DELETE FROM lecture_daily_watch_stats;
 DELETE FROM lecture_watch_stats;
+DELETE FROM publish_medium_watch_stats;
 DELETE FROM unknown_video;
 
 CREATE OR REPLACE PROCEDURE temp_count_lecture_view(lec_id int, watch_timestamp timestamp) AS $$
@@ -58,6 +59,7 @@ DO $$
 
             IF processed_count % 10000 = 0 THEN
                 RAISE NOTICE '(hlslog) Processed %/% (% %%)', processed_count, total_processing_count, (processed_count::double precision / total_processing_count * 100)::int;
+                COMMIT;
             END IF;
             SELECT processed_count + 1 INTO processed_count;
 
@@ -91,6 +93,7 @@ DO $$
 
             IF processed_count % 10000 = 0 THEN
                 RAISE NOTICE '(log) Processed %/% (% %%)', processed_count, total_processing_count, (processed_count::double precision / total_processing_count * 100)::int;
+                COMMIT;
             END IF;
             SELECT processed_count + 1 INTO processed_count;