unify migration scripts

Related: https://pagure.io/koji/issue/3623

docs/schema-update-1.29-1.30.sql

@@ -4,10 +4,4 @@
 
 BEGIN;
 
--- clean some unused old indices if they still exist
--- https://pagure.io/koji/issue/3160
-DROP INDEX IF EXISTS image_listing_archives;
-DROP INDEX IF EXISTS image_listing_rpms;
-DROP INDEX IF EXISTS imageinfo_listing_rpms;
-
 COMMIT;

docs/schema-upgrade-1.29-1.30.sql

@@ -10,4 +10,10 @@ UPDATE archivetypes set compression_type='zip' WHERE name = 'jar';
 UPDATE archivetypes set compression_type='zip' WHERE name = 'zip';
 UPDATE archivetypes set compression_type='tar' WHERE name = 'tar';
 
+-- clean some unused old indices if they still exist
+-- https://pagure.io/koji/issue/3160
+DROP INDEX IF EXISTS image_listing_archives;
+DROP INDEX IF EXISTS image_listing_rpms;
+DROP INDEX IF EXISTS imageinfo_listing_rpms;
+
 COMMIT;