Revert _meta addition to prompt config fields in migration docs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: chughtapan

docs/migration-SKILL.md

@@ -259,7 +259,7 @@ server.registerPrompt(
 );
 ```
 
-Config object fields: `title?`, `description?`, `argsSchema?`, `_meta?`
+Config object fields: `title?`, `description?`, `argsSchema?`
 
 ### Resources