FIX old index name

lib/Migration/Version030102Date20210812020000.php

@@ -33,6 +33,7 @@ class Version030102Date20210812020000 extends SimpleMigrationStep {
 
         // old indexes remain in SITIV database
         if ($table->hasIndex('dematpayslip_archive_pastell_id_document')) {
+            $table->dropIndex('dematpayslip_archive_pastell_id_document');
             $table->addUniqueIndex(['pastell_id_document'], 'demat_archive_pastell_id_doc');
         }
         if ($table->hasIndex('dematpayslip_archive_id_user')) {