Remove duplicate directus_migrations collection (#8383)

The collection is already defined on line 29.

api/src/database/system-data/collections/collections.yaml

@@ -57,6 +57,5 @@ data:
     display_template: '{{ first_name }} {{ last_name }}'
   - collection: directus_webhooks
     note: $t:directus_collection.directus_webhooks
-  - collection: directus_migrations
   - collection: directus_dashboards
   - collection: directus_panels