updated comments on tmp sql migration to use CREATE..AS..SELECT per a…

…greement on pr feedback for using this mechanism

services/horizon/internal/db2/schema/migrations/57_txsub_read_only.sql

@@ -4,9 +4,10 @@ DROP TABLE txsub_results;
 
 -- used to temporarily store filtered-out transactions
 -- needed by the transaction system
--- TODO - is this acceptable to do CREATE..SELECT..AS, 
+--  
 -- any future migrations that would change history_transactions
 -- require dropping history_transactions_filtered_tmp, and rerunning this CREATE..SELECT..AS
+-- to keep the tmp table in sync with schema.
 CREATE TABLE history_transactions_filtered_tmp AS 
   select * FROM history_transactions
   WHERE ledger_sequence IS NULL;