Remove migration 158 repair reference from docs

The migration archaeology has been squashed. Migration 142/158 memo
repair is no longer relevant since the base migration (106) now includes
memo from the start.

Part of migration squash for 2.0.0 release.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: durable-workflow-ops

docs/migration.md

@@ -161,9 +161,7 @@ composer update durable-workflow/workflow
 php artisan migrate
 ```
 
-If you upgraded from an early v2 pre-release that ran migration 142 without the `memo` column on `workflow_run_summaries`, migration 158 will detect and repair the missing column automatically. No manual intervention is needed.
-
-If you previously published migration files, you may need to publish the new ones or switch to auto-loaded migrations.
+The 2.0.0 release includes 19 clean base table migrations. If you previously published migration files, you may need to publish the new ones or switch to auto-loaded migrations.
 
 ## Backend capability check